Hardened inductive device and systems and methods for protecting the inductive device from catastrophic events

ABSTRACT

A hardened inductive device and systems and methods for protecting the inductive device from impact is provided. The inductive device is hardened with protective coating and/or an armor steel housing. The hardened inductive device is protected from impact by an object such as a bullet and leakage of dielectric fluid is prevented. Acoustic and vibration sensors are provided to detect the presence and impact, respectively, of an object in relation to the inductive device housing. The measurements of the acoustic and vibration sensors are compared to thresholds for sending alarms to the network control center and initiating shut-down and other sequences to protect the active part. The acoustic sensor results are utilized to determine the location of origin of the projectile.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional patentapplication Nos. 62/068,495 filed on Oct. 24, 2014 and 62/238,196 filedon Oct. 7, 2015, which are hereby incorporated by reference in theirentirety.

FIELD OF INVENTION

The present application is directed to an inductive device that canwithstand a catastrophic event.

BACKGROUND

Inductive devices such as power transformers and other electricalequipment are often located outdoors and subject to environmental,animal and human factors. In particular, nefarious acts by humans andextreme weather may cause damage to electrical equipment locatedoutdoors (not in a building). Even seismic events may cause damage tothe transformers. The damage may take considerable time to remedy andput the electrical equipment back in service, potentially causing apower outage.

SUMMARY

An inductive device has a tank with top, bottom and side walls and eachof the top and side walls has an outer substrate surface. A core havingat least one core limb extending between a pair of yokes, at least onecoil assembly mounted to the at least one core limb, and an insulatingmedium are disposed in an internal volume of the tank. A coating layeris bonded to the tank side wall outer substrate surfaces. The coating isa polyurea coating upon reaction and is formed of first and secondcomponents prior to reaction. The first component is an aromaticisocyanate mixture, an aromatic diisocyanate, an aliphatic isocyanatemixture or an aliphatic diisocyanate. The second component is an aminemixture or a polyamine.

A system is provided to detect the approach to and/or impact of anobject on electrical equipment that has a housing of a top wall, abottom wall, and at least one side wall. The system has the electricalequipment, at least one acoustic sensor for measuring the sound pressureof the object approaching the electrical equipment, at least onevibration sensor for measuring the acceleration of the electricalequipment housing surface caused by the object striking the housing, atleast one processor, and a non-transitory computer readable storagemedium having thereon a plurality of machine-readable instructions thatwhen executed by at least one computer processor cause the at least onecomputer processor to compare signals received from the acoustic andvibration sensors against thresholds for sound pressure and accelerationto determine whether impact by the object to the electrical equipmenthas occurred. The at least one acoustic sensor is in a predeterminedlocation not in contact with the housing and the at least one vibrationsensor is in a predetermined location in contact with the electricalequipment housing.

A system is provided for determining the location of impact of an objectto at least one wall of electrical equipment. The electrical equipmenthas a housing of a top wall, a bottom wall, and at least one side wall.The system has the electrical equipment, at least two vibration sensorsfor measuring the acceleration of the electrical equipment housingsurface caused by the object striking the housing, at least oneprocessor, and a non-transitory computer readable storage medium havingthereon a plurality of machine-readable instructions that when executedby the at least one computer processor cause the at least one computerprocessor to compare signals received from the vibration sensors againstthresholds for acceleration to determine the location of object impactto the electrical equipment at least one wall. The at least twovibration sensors are in contact with the electrical equipment housingand spaced apart from one another on a single wall of the electricalequipment housing.

A system for determining the location of origin of an object withrespect to electrical equipment. The system has the electrical equipmenthaving a housing comprised of a top wall, a bottom wall, and at leastone side wall, acoustic sensors arranged in a tetrahedral configurationfor measuring the sound pressure of the object approaching theelectrical equipment, at least one processor, and a non-transitorycomputer readable storage medium having thereon a plurality ofmachine-readable instructions that when executed by the at least onecomputer processor cause the at least one computer processor to performthe following steps when one of the azimuth and elevation angles inrelation to the object origin is known: determining the one of theazimuth and elevation angles that is unknown based on time of arrival ofthe muzzeblast and shockwave associated with the object with relation toeach of the acoustic sensors; and using the azimuth and elevation anglesto determine the distance to the object origin. The acoustic sensors arearranged out of contact with the electrical equipment housing.

A method for protecting an inductive device upon detection of impact tothe inductive device is provided. The method has the following steps: a.detecting that at least one of sound pressure, vibration, insulatingmedium temperature, insulating medium pressure, and insulating mediumlevel of the inductive device is at an actionable level; b. closingvalves to a primary cooling system of the inductive device; and c.opening valves to a secondary cooling system.

A system for providing secondary cooling to an inductive device has aninductive device having a core having at least one core limb extendingbetween a pair of yokes, at least one coil assembly mounted to the atleast one core limb, an insulating medium disposed in an internal volumeof a tank and a tank with top, bottom and side walls; a device formeasuring at least one of insulating medium temperature, insulatingmedium pressure, and insulating medium level; primary and secondarycooling systems, each having: at least one fan, a radiator or cooler andat least one valve to control the flow of the insulating medium; and anon-transitory computer readable storage medium having thereon aplurality of machine-readable instructions that when executed by atleast one computer processor cause the at least one computer processorto compare at least one of oil temperature, oil pressure, and oil levelas measured by the measuring device against a predetermined thresholdfor at least one of the insulating medium temperature, insulating mediumpressure, and insulating medium level measurements.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, structural embodiments are illustratedthat, together with the detailed description provided below, describeexemplary embodiments of a hardened inductive device and systems andmethods for protecting the inductive device from catastrophic events.One of ordinary skill in the art will appreciate that a component may bedesigned as multiple components or that multiple components may bedesigned as a single component.

Further, in the accompanying drawings and description that follow, likeparts are indicated throughout the drawings and written description withthe same reference numerals, respectively. The figures are not drawn toscale and the proportions of certain parts have been exaggerated forconvenience of illustration.

FIG. 1 is a perspective view of an inductive device embodied inaccordance with the present disclosure;

FIG. 2 is a side view of the inductive device having a shield around theconservator;

FIG. 3 is a side view of the inductive device showing a reinforcedmanhole cover;

FIG. 4a is a top view of an exemplary tank used in testing the impactresistance of the inductive device after application of a coating to thetank walls and hardening;

FIG. 4b is a front view of the tank of FIG. 4 a;

FIG. 4c is a side view of the tank of FIG. 4 a;

FIG. 5a is a top view of a plate assembly for retrofit applications usedin ballistic testing;

FIG. 5b is a bottom view of the plate assembly for retrofit applicationsof FIG. 5 a;

FIG. 5c is a side view of the plate assembly for retrofit applicationsof FIG. 5 a;

FIG. 6 shows hardened steel plates secured by a bracket for protecting agas relay of the inductive device;

FIG. 7a shows the oil and pressure level sensor having a ballisticshield installed to protect the oil and pressure level sensor fromballistic impact;

FIG. 7b shows mounting brackets for the ballistic shield;

FIG. 7c shows a partially assembled ballistic shield;

FIG. 7d shows the ballistic shield assembled around the oil and pressurelevel sensor;

FIG. 8a depicts OFAF (forced oil/forced air heat exchanger) coolersmounted to the tank of the inductive device and having ballistic plates;

FIG. 8b depicts the OFAF cooler vertically directed fans;

FIG. 9 is a perspective view of the inductive device having mobilecoolers protected by ballistic plates;

FIG. 10 is a chart of acoustic measurements taken at various measurementpoints in relation to an operating inductive device coated with thecoating;

FIG. 11 shows the measurements used to calculate the total core noisefor the coated transformer;

FIG. 12a shows a ballistic barrier surrounding a valve of the inductivedevice;

FIG. 12b shows a ballistic barrier surrounding a tap changer;

FIG. 13 is a schematic of one embodiment of a sensor-based ballisticimpact detection system for electrical equipment in accordance with thepresent disclosure;

FIG. 14 is flow chart of a method for obtaining, processing, andclassifying sensor data for determining whether to issue an alarm ortrigger detailed recording of sensor data;

FIG. 15 depicts a system for sensing impact and/or approach of an objectto electrical equipment and determining whether the impact to theelectrical equipment is actionable;

FIG. 16 depicts the setup of ballistic test trials using a transformertank having raw vibration, root mean square (RMS) vibration, andacoustic sensors installed nearby or in contact with the tank;

FIG. 17 depicts the location of projectile strikes in test trials uponthe impact of the projectiles to the tank;

FIG. 18 is a plot of the acceleration vs. time results of the rawvibration and RM sensors of bullet trial 4;

FIG. 19 is a plot of the acoustic sensor sound pressure test results ofbullet trial 4;

FIG. 20 is a chart for converting sound pressure measurements obtainedin Pascals to Decibels.

FIG. 21 is a plot of the acoustic signature of trial 4 including theshockwave and the muzzle blast;

FIG. 22 is a plot of the acoustic signature of trial 4 including theshockwave and the impact;

FIG. 23 is a plot of the rock trial acceleration versus time as measuredby the raw vibration and acoustic sensors;

FIG. 24 is a plot of the rock trial acoustic signature as measured bythe acoustic sensor for rock trial 1;

FIG. 25 is a plot of the hammer trial 2 acceleration versus time asmeasured by the raw vibration and RMS sensors;

FIG. 26 is a plot of the hammer trial 2 acoustic signature;

FIG. 27 is a plot of the bullet trial 4 acceleration versus time asmeasured by the raw vibration and RMS sensors;

FIG. 28 is a plot of the max raw acceleration versus caliber of rocksversus hammers as measured by raw vibration sensors;

FIG. 29 is a plot of the max raw acceleration versus caliber of rocksversus hammers versus bullets as measured by raw vibration sensors;

FIG. 30 is a plot of the max pressure versus caliber of rocks versushammers as measured by the acoustic sensor;

FIG. 31 is a plot of the RMS acceleration versus time for bullet versusnon-bullet impacts to the transformer tank also showing the time decayof the signals;

FIG. 32a is a zoomed in plot of the FIG. 32b sound pressure versus timefor bullet versus non-bullet impacts to the transformer tank;

FIG. 32b is a plot of sound pressure versus time for bullet versusnon-bullet impacts to the transformer tank;

FIG. 33 is a plot of average pressure over the last four measured valuesversus time for an average ballistic trial (such as trial 4);

FIG. 34 shows the muzzle blast superimposed over the hammer impact foran average ballistic trial versus the second hammer trial;

FIG. 35 shows a tetrahedral array that may be used to generate multiplegunshot time of arrival measurements;

FIG. 36 shows the results of a method for residual search for the originof a projectile;

FIG. 37 shows a possible arrangement of the acoustic sensors as arectangular tetrahedron;

FIG. 38 provides parameters for shot origin detection when variouslocations and numbers of acoustic sensors are used;

FIG. 39 is a plot of acceleration versus time for the bullet impact oftrial 5 as measured by the raw vibration and RMS sensors;

FIG. 40 is a plot of acceleration versus time for the bullet impact oftrial 12 as measured by the raw vibration and RMS sensors;

FIG. 41 is a plot of shot impact localization for projectile trial 6;

FIG. 42 is a plot of shot impact localization for projectile trial 12;

FIG. 43 is a schematic of a response sequence upon detection of low oillevel and/or low oil pressure in the inductive device during anactionable event;

FIG. 44 is a top view of the inductive device having removable ballisticpanels;

FIG. 45 is a top view of the inductive device having a ballisticbarrier;

FIG. 46 is a side view of the inductive device having aballistic-resistant blanket protecting the conservator, bushings andsurge arresters;

FIG. 47 is a top view of the inductive device having stiffeners to whichballistic-hardened plates are connected;

FIG. 48 is a top view of the inductive device having a ballisticresistant blanket covering the conservator, bushings, surge arrestersand instrumentation of the inductive device; and

FIG. 49 is a side view of the inductive device having a ballisticbarrier surrounding the inductive device.

DETAILED DESCRIPTION

With reference to FIG. 1, an inductive device 10 such as transformerrated at 60 MVA or greater is shown. It should be understood that theinductive device 10 may be embodied as a power transformer, distributiontransformer or a shunt reactor and is single-phase or poly-phase, e.g.three-phase, depending upon the application. The inductive device 10 hashardening features described herein that are applicable to newlymanufactured transformers as well as may be retrofit to existingin-repair and in-service transformers.

The inductive device 10 is designed to address the areas that are proneto failure as a result of ballistic projectiles and other intrusions.Certain areas of the inductive device 10 are provided with protectivematerial to deflect direct hits, such as by a projectile whereas otherareas utilize sensors to detect damage and switch to back-up systems toprotect the core and coil windings. The core and coil windings, alsoknown as the active part of the transformer, have the longest lead timein terms of repair and/or replacement. A coating as described in moredetail below, when applied to the transformer tank 20, renders the tankwalls impervious to bullet penetration when combined with various gradesof steel used in forming the tank. The tank 20 and coating materials andthickness are optimized in the present disclosure to protect theinductive device 10 from impact and penetration by an object or otherintrusions.

The inductive device 10 has a tank 20, a core with at least one limbdisposed vertically between a pair of yokes and at least one coilassembly mounted to the at least one limb. The coil assembly has ahigh-voltage coil and a low-voltage coil. A first end of the at leastone coil assembly is connected to a high-voltage bushing 14 extendingfrom the cover of the tank 20. The core and the at least one coilassembly are disposed in an internal volume of the tank 20 along with aninsulating medium such as dielectric fluid or a gas such as sulfurhexafluoride (SF₆), nitrogen or air. In particular, the insulatingmedium may be mineral oil, natural or synthetic ester liquid. Fluidssuch as natural ester and synthetic liquids may provide fire and flashpoints that are more than twice the values of mineral oil, reducing therisk of fire in the event that the inductive device experiences impactby an object or another event occurs.

When the inductive device 10 is embodied as a shunt reactor, the shuntreactor is used to compensate reactive power and generally has a corewith one or more non-magnetic gaps in the at least one limb. Thenon-magnetic gaps in the at least one limb of the shunt reactor core maybe filled with an insulating material. There may be a non-magnetic gapin each limb of the core with the non-magnetic gaps positioned inside oroutside the corresponding winding assembly mounted to the at least onelimb.

A first end of the winding is connected to the bushing 12, 14 extendingfrom the top wall 21 of the tank 20. In one embodiment the bushings 12,14 are dry-type bushings and are not filled with dielectric fluid. Inthat same embodiment, the bushings are formed of hydrophobiccycloaliphatic epoxy resin, silicone insulator or another suitablematerial for the application. In this manner, if the bushings 12, 14receive impact from a projectile, the bushings are not susceptible toshattering and releasing oil, as in typical porcelain bushings.

Additionally, an electrical potential monitoring device may be providedwith the bushings 12, 14. Any damage to a porcelain or dry-type bushingis detected by the electrical potential monitoring device due to adetected change in the capacitance of the bushings 12, 14 and/or achange in the leakage current measured value. An alarm is provided toalert personnel to the detection of impact experienced by the bushings12, 14.

With continued reference to FIG. 1, the tank 20 is formed of sheet metalplates that are connected at seams 25 by welding or are bolted togetherusing fasteners. As will be described in more detail below, a coating ofpolyurea was applied to outer surfaces of the tank walls 23 as well asthe welds and interfaces between the metal plates of the tank 20.Alternatively, the tank 20 is formed from one single piece of sheetmetal by bending the metal to form corners and side walls 23 and thebends have the coating applied thereto. The tank 20 is rectangular,having a bottom wall, side walls 23, and a top wall 21. Alternatively,the tank is cylindrical, having a cylindrical side wall, a bottom walland a cover or top wall.

The inductive device 10 has the coating applied to outer surfaces ofside walls 23 to harden the exterior thereof and protect the core and atleast one coil assembly from damage due to impact or penetration of thetank 20 walls 23. It should be understood that any electrical equipmentin a substation such as rotating machines, switchgear, and circuitbreakers may have an exterior or enclosure having outer surfacesprotected by the coating in the same manner as the inductive device 10described herein. Further, the electrical equipment housing may beretrofit with ballistic-hardened plates in the same manner as theinductive device 10 as will be described in more detail below.

It should be understood that when the electrical equipment is embodiedas switchgear or a dead tank circuit breaker, the insulating medium maybe sulfur hexafluoride (SF₆), air or another type of insulating mediumsuitable for the application.

The inductive device 10 is hardened to address the areas that are proneto failure as a result of the impact of an object such as a ballisticprojectile and other intrusions. Certain areas of the inductive deviceare provided with the coating to prevent penetration of the tank in adirect impact by a projectile or other object. For instance, the tank 20is hardened because the tank 20 houses the core and coil assemblies,also known as the active part of the inductive device. The core and coilassemblies have the longest lead time in terms of repair and/orreplacement.

Also depicted in FIG. 1 are low-voltage bushings 12 and low-voltagesurge arresters, high-voltage surge arresters 16, a pressure reliefdevice 26, a control cabinet 28, housings 38, a sudden pressure reliefvalve 30, oil fill fitting 37, oil drain valve 39, and a regulatednitrogen gas supply 40 for maintaining a positive pressure nitrogen gasblanket in the gas space of the inductive device 10 which is inside theinternal volume of the tank between the top oil level and the tank 20cover.

A radiator cooling system 22 having an upper radiator valve 34, a lowerradiator valve 36, and fans 18 cools the inductive device 10 duringoperation, and oil level and pressure gauges 24 work in conjunction withthe back-up water cooling system 33 to cool the inductive device 10. Inthe case of the inductive device cooling radiators becoming punctured byan object such as a projectile, the oil level and pressure sensor 24detects the drop in oil pressure and enacts a sequence of valveactuations designed to protect the active part of the inductive device10 from being damaged. The oil level and pressure sensor 24 may beprovided as a combined sensor or separate sensors. By way ofnon-limiting example, an oil level sensor that may be used with thepresent disclosure is the oil level indicator eOLI available from Comemof Montebello Vicento, Italy. Further by way of non-limiting example,pressure sensors that may be used with the present disclosure are theQUALITROL 032/042/045 and AKM 44712/34725 large oil level indicatorsavailable from Qualitrol of Fairport, N.Y.

Types of steel used in forming the inductive device tank 20 are mildsteels such as CSA G40.21 grade 50W steel, mild steel that meets theASTM A36 standard, mild steel meeting the ASTM 504 standard, and mildsteel that meets the A572 Grade 50 standard, although it should beunderstood that other types of steel may be used. The thickness of themild steel used in the tank 20 is from about 0.375 inches to about 1.25inches in thickness.

Chemical compositions of the A36 and A572 grade 50 mild steels in weightpercent based on total weight are provided by way of non-limitingexample in Tables 1 and 2 below:

TABLE 1 Chemical Composition - Steel ASTM A36 Element Min Max Carbon —0.29 Manganese 0.85 1.35 Phosphorous — 0.04 Sulfur — 0.05 Silicon — 0.4Copper 0.2  —

TABLE 2 Chemical Composition - Steel ASTM A572 grade 50 Element Min MaxCarbon — 0.23 Manganese — 1.35 Phosphorous — 0.04 Sulfur — 0.05 Silicon— 0.4 Copper 0.2 — Nb 0.005 0.05

The ASTM 36 and ASTM A572 grade 50 mild steel used to construct the tank10 has the following composition in weight percent based on totalweight:

-   -   0%≤carbon≤0.29%;    -   0.85%≤manganese≤1.35%;    -   0%≤phosphorous≤0.04%;    -   0%≤sulfur≤0.05%;    -   0%≤silicon≤0.4%;    -   At least 0.2% copper;

and the remainder being constituted by iron. Additionally, otherelements may be present in trace amounts. Mild steels meeting the ASTMA36 standard and the ASTM standard A572 Grade 50 have, in addition tothe ranges listed for the elements C, Mn, P, S and Si above, at least0.2% by weight percent of copper. Further, mild steel of ASTM standardA572 Grade 50, in addition to having the elements C, Mn, P, S, Cu andSi, includes in its composition from 0.005 to 0.05 niobium in weightpercent based on total weight.

The inventors of the present disclosure conducted tests using thecoating in combination with various metal substrates including mildsteel previously mentioned and AR500 steel (Abrasion Resistant (AR)steel with a Brinell hardness of 500). The inventors found throughtesting that the coating prevented projectiles such as the ammunitionprovided in Tables 6 from penetrating the inductive device tank 20 walls23. It should be understood that metal substrates include outer surfacesof inductive device tank 20 walls and any shielding 48, 56, 52, 78, 92provided for transformer components.

An optimized coating thickness used in conjunction with an optimizedtank wall thickness of ½ inch of AR500 steel was found to achieve a UL752 level 8 and a UL 752 level 10 of ballistic protection. An example ofAR500 steel that may be used in constructing the tank 20 is Tensalloy®Blue AR500 available from Clifton Steel Company of Maple Heights, Ohio.

The typical chemical composition of Tensalloy® Blue AR500 (having athickness of 0.236 inch to 2.5 inches) in weight percent based on totalweight is provided in Table 3 below:

TABLE 3 Carbon 0.31 Manganese 1.50 Phosphorous 0.025 Sulfur 0.015Silicon 0.50 Chromium 0.87 Nickel 0.70 Molybdenum 0.35 Boron 0.003

Alternatively, a standard composition of AR500 steel that may be used inconstructing the inductive device tank in weight percent based on totalweight is provided in Table 4 below:

TABLE 4 Carbon 0.30 Manganese 1.70 Silicon .70 Chromium 1.00 Nickel 0.8Molybdenum 0.50 Boron 0.004

In one embodiment a transformer tank 20 formed of AR500 steel having a ⅜inch thickness and no coating was found to achieve UL 752 ballisticlevel 8 protection, as will be described in further detail below.Additionally, the AR500 steel is used to harden the control cabinet 28,water cooling back-up system 33, barriers, and shields. The coatingreduces the amount of metal fragment “spall” as a result of the impactof a projectile. The coating may be used on all outer surfaces of thetank 20 such as side walls and cover, control cabinet 38, radiators 22,conservator 46, valves, housings, and bushings 12, 14.

Examples of the coating include but are not limited to: a pure polyureacoating, a two-component polyurea and polyurethane spray system, and anaromatic polyurea spray elastomer system having low or no volatileorganic compounds. The coating provides durable skin composition forresistance of corrosive chemicals and environmental factors. It shouldbe understood that other types of coatings are contemplated by theinventors and that the coating types are provided by way of non-limitingexample.

When the coating is embodied as a two-component polyurea spray elastomersystem with zero volatile organic compounds, a first component, the “A”side, comprises an aromatic or aliphatic isocyanate (or diisocyanate)and a second component, the “B” side, comprises an amine mixture or apolyamine. The aromatic isocyanate mixture contains from about 0.1percent to about 50 percent by weight of isocyanates based on totalweight. In particular, the isocyanate mixture contains from about 0.1percent to about 45 percent by weight diphenylmethane-4,4′-diisocyanateand from about 0.1 percent to about 5 percent by weight methylenediphenyl diisocyanate based on total weight. The amine mixture containsfrom about 70 percent to about 99 percent by weight amines, for examplediethylmethylbenzenediamine andalpha-(2-Aminomethylethyl)-omega-(2-aminomethylethoxy)-poly(oxy(methyl-1,2-ethanediyl)).More particularly, the amine mixture contains from about 50 percent toabout 75 percent by weight ofalpha-(2-Aminomethylethyl)-omega-(2-aminomethylethoxy)-poly(oxy(methyl-1,2-ethanediyl))and from about 20 percent to about 25 percent by weight ofdiethylmethylbenzenediamine.

A pigment may be added to the amine mixture at from about 0.1% to about20% by weight to provide the desired color of the coating. In oneembodiment, the coating has p-aramid fibers based on poly(p-phenyleneterephthalamide) dispersed with the polyurea coating during the sprayingprocess onto the substrate to provide added strength to the coating. Theuse of ‘about’ herein means plus or minus one percent.

The first and second components are preheated and applied at highpressure using dual component spray equipment in a 1:1 ratio. Thepreheated isocyanate and amine combine and react out of the spray gun athigh pressure to form a polyurea coating on the applied substratematerial. The polyurea coating that is a reaction product of the firstand second components, cures within a few minutes upon application andbonds to the substrate material, in the present case, mild steel orAR500 steel.

Alternatively, the coating is embodied as a two-component polyurea sprayelastomer system having a first component comprising an aromaticisocyanate mixture containing from about 30% to about 60% by weightpercent of isocyanates and from about 5% to about 15% by weight percentof propylene carbonate based on total weight. The isocyanates are areaction product of polyol with methylenediphenyl diisocyanate. A secondcomponent is an amine mixture containing from about 61 percent to about89 percent by weight polyoxypropylenediamine based on total weight.

The first and second components are preheated and applied at highpressure using dual component spray equipment in a 1:1 ratio. Thepreheated isocyanate and amine components combine and react out of thespray gun at high pressure to form a polyurea coating on the appliedsubstrate material. The polyurea coating that is a reaction product ofthe first and second components, cures within a few minutes uponapplication and bonds to the substrate material, in the present case,mild steel or AR500 steel.

An example of a coating for use in carrying out the present disclosureis XS-350 available from Line-X Protective Coatings of Huntsville, Ala.Other examples of coatings that may be used to carry out the teachingsof the present disclosure are Dragonshield-BC available from SpecialtyProducts, Inc. of Lakewood, Wash. and RhinoArmor PPFR 1150 availablefrom Rhino Linings of San Diego, Calif. It should be understood thatvarious coatings are contemplated by the inventors and that the coatingtypes are provided by way of non-limiting example.

The coating has an ASTM D2240 shore D durometer hardness of from about45 to about 70. More particularly, the shore D durometer hardness isfrom about 50 to about 61.

The inventors of the present disclosure applied the coating to a 69 kV,12/16/20 MVA (ONAN/ONAF/ONAF) transformer that had previously been inservice. The inductive device 10 was de-energized, the dielectric fluidin the tank 20 was drained, and the radiators and all externalaccessories such as conduits and wiring were removed prior to theapplication of the coating.

The coating was applied using a spray gun to achieve a wet filmthickness of from about 20 mils to about 40 mils (0.5 mm to 1 mm) foreach coat to achieve at least a one-half inch thickness on each of thetank walls.

The first series of ballistic tests conducted by the inventorsinvestigated the performances of various thicknesses of mild steelplates (⅛″, 5/16″, ⅜″ and ½″) with different thicknesses of coating (⅛″,¼″ and ½″) applied and bonded to one side of the steel plate substrate.The tests were performed according to ASTM-F1233 using two types ofammunition—7.62 mm (.308 caliber) NATO M80 Ball, full metal jacket (FMJ)and 30-06, jacketed soft point (JSP) bullets. The descriptions of theASTM tests on the plate samples are shown in Table 5.

TABLE 5 Sample Description for Test Series #1 Coating Thicknesses ⅛ in ¼in ½ in Plate Thicknesses NA (blank) (3.175 mm) (6.35 mm) (12.7 mm) ⅛inch (3.175 mm) 1A 1B 1C 1D 5/16 inch (7.9 mm) 2A 2B 2C 2D ⅜ inch (9.5mm) 3A 3B 3C 3D ½ inch (12.7 mm) 4A 4B 4C 4D

TABLE 6 Ballistic Test Comparison, ASTM F1233 and UL Level 8 Weight MinVelocity Max Velocity Range to Rating Ammunition (grains) (ft/s) (ft/s)# Shots target (ft) ASTM-F1233 R3 7.62 mm (.308 149 2700 2800 3 25 .30cal. 7.62 caliber) M80, Ball NATO M80 ASTM F1233 R2 30-06, Springfield,180 2850 3000 3 25 .30 cal. 30-06 JSP JSP UL Level 8 7.62 mm Rifle Lead150 2750 3025 5 15 Core Full Metal Copper Jacket Military Ball (.308Caliber)

All samples with steel thicknesses of ⅜ inch and thinner failed everytest regardless of the thickness of applied coating. A sample fails aparticular ballistic rating if there is one or more instance ofpenetration of the surface impacted by the prescribed ammunition. Thesamples having a ½ inch thick coating, a ¼ inch thick coating and lessthan those values each passed the ASTM-F1233 R3 test, but failed theASTM-F1233 R2 test. The ½ inch thick steel sample with a ½ inch coatingthickness passed both of the ASTM-F1233 R2 and ASTM-F1233 R3 ballistictests.

A comparison of characteristics of the ASTM-F1233 tests and UL 752 Level8 test is shown in Table 6. ASTM-F1233 R2 uses a heavier ammunition witha soft tip for better penetration of the target material and theammunition travels at a higher average velocity at impact than the ULLevel 8 ammunition. UL 752 Level 8 requires a closer range to targetthan the ASTM tests.

The ability to penetrate a material depends on several factors: thehardness and thickness of the material, the construction and weight ofthe bullet, and the impact velocity of the bullet on the material. Thestrength of impact and its ability to breach the material is dependenton the kinetic energy of the bullet, which is proportional to theproduct of its mass and square of velocity. For example, the averagekinetic energies upon impact for the UL 752 Level 8 ballistic and theASTM F1233 R2 ballistic are 2805 ft-lbs and 3436 ft-lbs, respectively.

The results of the ASTM F1233 tests are provided below for test series1:

TABLE 7 Summary of Results - Test Series 1 Steel Type Steel CoatingMedium ASTM (AS-Armor Thickness Thickness behind F1233 MS-Mild) (inches)(inches) wall Spec. Penetration MS ⅜ 0 Air R2 Yes MS ⅜ ⅛ Air R2 Yes MS ⅜¼ Air R2 Yes MS ⅜ 0 Air R2 Yes MS ⅜ ⅛ Air R2 Yes MS ⅜ ¼ Air R2 Yes MS ⅜½ Air R2 Yes MS ⅜ 0 Air R3 Yes MS ⅜ ⅛ Air R3 Yes MS ⅜ ¼ Air R3 Yes MS ⅜½ Air R3 Yes MS ½ 0 Air R2 Yes MS ½ ⅛ Air R2 Yes MS ½ ¼ Air R2 Yes MS ½½ Air R2 No MS ½ 0 Air R3 No MS ½ ⅛ Air R3 No MS ½ ¼ Air R3 No MS ½ ½Air R3 No

With reference now to FIGS. 4a, 4b, and 4c , test samples for testseries 2 were formed in the shape of cubes to mimic the general shape ofa transformer tank. The samples were constructed from mild or AR500steels having thicknesses of ⅜ inch and ½ inch as indicated in Table 8.Two lifting hooks 73 were provided on the top of each cube to allowcarrying by two people with a pole through the hooks. Two ports 71 wereprovided in the top of the cube for filling with water and for ventingdisplaced air out of the cube. All but two of the cubes were filled withwater to emulate dielectric fluid inside a transformer.

It should be noted that while water was used to fill the cubes and mimican incompressible fluid such as dielectric fluid, that dielectric fluidhas a greater viscosity than water. Therefore, the dielectric fluidwould be less likely to leak than water. However, due to safety andenvironmental concerns water was used in the testing rather thandielectric fluid. A comparison of the viscosities of dielectric fluidswith the viscosity of water is provided in the table below:

Kinematic Viscosity at 40° C. Fluid (mm²/s) Mineral Oil 9 Natural Ester28 Synthetic Ester 36 Water 0.658

One side of each cube was formed of bare metal, while the other threesides were each coated with the polyurea coating to achieve differentthicknesses as shown in the tables that follow. The top cover of thecube was secured with bolts onto a gasketed flange around the top of thecube. The cubes were rotated so that all coating thickness and metalthickness combinations faced the shooter for each test.

Samples for UL 752 ballistics tests were prepared as indicated in thetable below:

-   -   Sample #1—⅜″ Regular Steel Cube Filled with Water

Test Coating Thickness Ballistics Side Sequence (mils) Level D 1 1000UL-8 C 2 750 UL-8 B 3 500 UL-8 A 4 Blank UL-8

-   -   Sample #2—⅜″ Armor Steel Cube Filled with Water

Test Coating Thickness Ballistics Side Sequence (mils) Level A 1 BlankUL-8 D 2 750 UL-9 C 3 500 UL-9 B 4 250 UL-9

-   -   Sample #3—½″ Armor Steel Cube Filled with Water

Test Coating Thickness Ballistics Side Sequence (mils) Level D 1 1000UL-10 C 2 750 UL-10 B 3 500 UL-10 A 4 Blank UL-9

With reference now to FIGS. 5a, 5b, and 5c , test samples numbered 4 and5 in table 8 were prepared having parallel plates for retrofitapplications. In testing the retrofit applications, a ⅜ thick mild steelplate was used to emulate a transformer tank 20 and was offset by 8inches from a ⅜ inch AR500 armor steel plate 31 using an 8 inch widebrace 29. The test sequence was performed at UL 752 level 8 and UL 752level 9. The offset of 8 inches was used to mimic offset of theballistic protection plates from the tank wall by stiffeners 54 that are8 inches in width. The wall stiffeners 54 are rectangular prisms with anopen face that are welded onto the tank wall at equal spacing from oneanother. The wall stiffeners may be disposed vertically or horizontallywith respect to the plane of the bottom wall of the tank 20. Thestiffeners 54 may form gap with respect to the tank 20 wall and befilled with a ballistic-resistant material 74 such as Kevlar or sand.

As previously mentioned, different standards associations have developedratings for materials and structures that prevent penetration by certainammunitions fired from specified distances from the target. The secondseries of tests performed by the inventors of the present disclosureevaluate combinations of mild steel and AR500 steel tank thicknessescoated with the coating at varying thicknesses. The combinations of tankmaterial, tank thickness, and coating thickness were tested according tothe three highest levels of the UL752 standard, UL752 levels 8, 9 and10.

The specifications for the UL752 standard levels 8, 9, and 10 aredescribed as follows:

UL Level 8 is tested using a 30 caliber, M80 Ball Full Metal Jacket(FMJ) with 166 grains travelling at a velocity of 2,750-3,025 feet persecond. Five shots are fired into the sample placed 15 feet from themuzzle of the gun.

UL Level 9 is tested using a 30 caliber, Armor Piecing (AP), M2 bulletwith 166 grains travelling at velocity of 2715-2986 feet per second. Oneshot is fired into the sample placed 15 feet from the muzzle of the gun.

UL Level 10 is tested using a 50 caliber, ball with 708 grainstravelling at velocity of 2810-3091 feet per second. One shot is firedinto the sample placed 15 feet from the muzzle of the gun.

All samples were tested using the required number of shots fired along ahorizontal plane orthogonal to the transformer tank 20 walls located ina vertical plane.

The optimal coating and tank wall thickness combination for UL Level 10was found to be ½ inch thick coating applied to tank walls formed ofAR500 steel having a ½ inch thickness as shown in Table 8 when theXS-350 two-component polyurea spray was used as the coating. When thecoating of at least ½ inches was applied to the AR500 steel tank havingat least a ½ inch thickness, shrapnel from the ballistic impact wasmostly trapped inside the coating and did not penetrate the AR500 steeltank 20. The coating appeared to have absorbed a significant amount ofthe shrapnel thus reducing the amount of spall from the tank surface. Inaddition, the AR500 steel wall protected the bullet from penetrating thetank walls and reaching the inside of the tank.

The results of ballistics testing carried out by the inventors inaccordance with the UL 752 standard are presented in table 8.

TABLE 8 Ballistic testing in accordance with the UL 752 Standard SteelType Steel Coating Medium UL Pen- Sample (AS-Armor Thickness Thicknessbehind Rating etra- ID MS-Mild) (inches) (inches) wall Tested tion 5 AS⅜ 0 Air 8 No 1A MS ⅜ 0 Water 8 Yes 1B MS ⅜ ½ Water 8 Yes 1C MS ⅜ ¾ Water8 Yes 1D MS ⅜ 1 Water 8 Yes 1E MS ½ ½ Water 8 Yes 2A AS ⅜ 0 Water 8 No2B AS ⅜ ¼ Water 9 Yes 2C AS ⅜ ½ Water 9 Yes 2D AS ⅜ ¾ Water 9 Yes 3A AS½ 0 Water 9 No 4 AS ⅜ ¼ Air 9 No 3B AS ½ ½ Water 10 No 3C AS ½ ¾ Water10 No 3D AS ½ 1 Water 10 No

In summary, Table 8 provides the following results. AR500 steel having a⅜ inch thickness meets UL level 8 ballistic requirements without anycoating and resulted in a little damage at the impact site on the tank20. AR500 steel having ½ inch thickness with no coating meets UL level 9ballistic requirements, but experienced significant damage to the impactsite. AR500 steel having ½ inch thickness and ½ inch applied polyureacoating meets UL level 10 ballistic requirements.

Further, in the samples formed of mild steel having a ⅜ inch thicknessand the coating applied to an at least a ½ inch thickness, the tankwalls were penetrated by the UL 752 level 8 ammunition and experiencedat least ½ inch diameter holes in the tank. However, there was only amere trickle of water through the coating. Therefore, a tank 20 with thecoating applied is less likely to leak dielectric fluid through any tinyholes.

For example, an opening having a diameter of from about 0.5 mm to about12.7 mm in the tank wall is prevented from leaking dielectric fluid fromthe tank. The defects in welds at joints connecting side walls 23 of theinductive device may be the size of a pinhole and closer to from about0.5 mm to about 1 mm in diameter whereas the size of a bullet hole isfrom about 5 mm to about 12.7 mm. In the case of the pinholes, thepinholes are filled or covered by the polyurea coating layer and leakingof dielectric fluid is prevented. In the case of bullet holes, thedielectric fluid leaks at mere drops at a time, preventing some impactto the environment by the leaking of dielectric fluid.

Further, the polyurea coating may provide a controlled rupture in theevent of an internal arc wherein pressure from the arc would be absorbedby the coating along the tank walls vertically and expose the weakestjoints at the tank cover 21 interface 27 where there is no coatingapplied. The controlled rupture properties can be tested by simulatinghigh energy arcs in tanks having coating and without coating applied tothe walls. A controlled rupture at the tank cover 21 interface 27 ismore desirable than a rupture at the side wall 23 welds 25, because thiscontrols oil leakage and supply of fuel to a fire in case of ignition.

A short circuit in a tank can be simulated by connecting a thin wirebetween two electrodes about one inch apart and fixed inside the tank. Ahigh energy arc can be simulated by passing high current through the twoelectrodes and the wire. The high current through the shorted circuitwill produce an arc with accompanying high pressure in the tank. If thearc energy is high enough the pressure can rupture the tank. In the caseof tank rupture, the rupture would be a controlled rupture at the tankcover 21 interface 27 due to the polyurea coating absorbing the pressurealong the tank walls vertically.

In summary, and as shown in tables 9, 10, and 11 below, the inventorsdiscovered through ballistic testing of mild and AR500 steel plates andtanks 20 that an optimized coating thickness of at least ½ inch appliedto an optimized tank thickness of ½ inch thick AR500 steel achieved upto UL 752 level 10 protection and limit spalling of metal fragments.However, some protective benefit was determined using at least a 0.25inch (6.35 mm) coating thickness and up to about a one inch (25.4 mm)coating thickness in combination with all of the various metals andthicknesses mentioned herein. As most inductive device tanks today areformed of mild steel, only newly manufactured inductive devices can beformed of AR500 steel tanks. Existing inductive devices can be retrofitwith AR500 steel plates having a polyurea coating of at least ½ inch inthickness.

Further, in an inductive device having a mild steel tank that isretrofit for withstanding a ballistic impact, the inductive device hasstuds welded to the tank 20 side walls to which AR500 steel plateshaving up to a 0.5 inch thickness are further bolted or welded toprovide a wall of protection. Alternatively, the AR500 steel plateshaving up to a thickness of 0.5 inch are welded or bolted to stiffeners54 attached longitudinally to the side walls of the tank. The coating isfurther applied to the AR500 steel plates until a thickness of at least0.5 inch is achieved. In order to provide UL level 8 ballisticprotection, the AR500 steel plates are provided in a ⅜ inch thicknessand at least 0.5 inch thick polyurea coating is applied thereto to limitspalling of metal fragments.

A summary of the solution for hardening new and retrofit inductivedevices is provided below.

TABLE 9 New Inductive device Application UL Ballistic Level Construction8 ⅜″ Armor Steel Tank + application of ½″ Coating 9-10 ½″ Armor SteelTank + application of ½″ Coating

TABLE 10 Retrofit Applications for ⅜″ Mild Steel Tank Walls UL BallisticLevel Construction 8 ⅜″ Armor Steel Panels attached to Tank Walls 9 ⅜″Armor Steel Panels, with applied ½″ Coating and attached to Tank Walls10 ½″ Armor Steel, with applied ½″ Coating and attached to Tank Walls

TABLE 11 Retrofit Applications for ½″ Mild Steel Tank Walls UL BallisticLevel Construction 8 Field Application of ½″ Coating to Tank Walls OR ⅜″Armor Steel Panels attached to Tank Walls 9 ⅜″ Armor Steel Panels, withapplied ½″ Coating and attached to Tank Walls 10 ½″ Armor Steel, withapplied ½″ Coating and attached to Tank Walls

In one embodiment, a first layer of the coating is bonded to the tankwalls and a steel plate is provided as a second layer. A third layer isprovided of the coating. The tank 20, first layer of coating, secondlayer of steel plate, and third layer of coating are bonded together.The first and third layers of coating are provided at thicknesses offrom about 0.25 inches (6.35 mm) to about 0.75 inches (19.05 mm). Thesteel plate formed of AR500 or mild steel of the types mentioned hereinis from about 0.25 inches (6.35 mm) to about 0.75 inches (19.05 mm).

Referring now to FIG. 2, an oil conservator 46 is shown having aballistic-resistant shield 48 attached thereto. The conservator shield48 is formed of AR500 steel or mild steel of the types mentioned abovein new and retrofit installations. When AR500 steel is utilized to forma conservator shield, the thickness of the steel is at least ⅜ inchesthick if AR500 is used alone to satisfy UL 752 ballistic level 8.Otherwise, 0.5 inch (12.7 mm) thick AR500 steel is used in conjunctionwith a coating thickness of 0.5 inches (12.7 mm) to satisfy UL 752ballistic levels 9 and 10. The ASTM F1233 standard can be met with 0.5inch (12.7 mm) thick mild steel and 0.5 inch (12.7 mm) thick coating.

The ballistic-resistant shield 48 is removable or fixed to theconservator 46 supports and/or tank 20. The ballistic-resistant shield46 also serves as camouflage for the conservator 46 as a potentialtarget is not visible and may be formed in a shape to deflectprojectiles. In one embodiment, the conservator 48 oil level gauge isprotected and hidden from view by a steel plate and can be read fromground level only or at a power network control center remote from ornearby the substation where the inductive device 10 is installed. Inanother embodiment, the conservator 48 is formed of mild steel having athickness of ½ inch and coated with the coating having a ½ inchthickness to meet ASTM F1233 R2 or R3 ballistic levels.

It should be understood that the tank 20 and conservator 46 may beformed of AR500 steel or heavy gauge steel in a new application, and thevalves, gauges and cooling systems may be placed in centrallocations/banks to be protected by various shielding formed of heavygauge or submarine steel. All surfaces may then be coated with thecoating and shields and barriers may be utilized instead of or inaddition to tank 20 and conservator 46 reinforced steel enclosures.Further, it should be understood that any combination made from thematerials and arrangements described herein may be utilized to hardenthe inductive device tank, provide a layered heterogeneous approach toshielding inductive devices 10 from projectiles, and that specificarrangements are provided by way of non-limiting example.

With reference now to FIG. 3, a manhole cover 58 is shown having a ⅜″AR500 steel manhole shield 56 in the same shape as the manhole coverbolted on top of the manhole cover 58 to the tank 20. The manhole shield56 bolsters the manhole cover 58 in the case of contact with aprojectile or other outside intrusion. The manhole shield 56 has lessfastener openings than the manhole cover 58 and is cut in a shape toaccommodate the existing fasteners that secure the manhole cover 58.

Referring now to FIG. 6, a frame 52 enclosing a gas relay 50, such as aBuchholz relay, is shown. The frame 52 is hardened and encloses the gasrelay 50 in both new and retrofit inductive device 10 installations andis secured to the gas relay by clamps 82 and a mounting bracket 84. Theclamps 82 have arcuate sides 86 to compensate for the flexing of thepipe 51. In one embodiment, the mild steel or AR500 steel frame 52 iscoated with the coating in the same thickness as previously describedfor the conservator shield 48. Further, it should be understood that themild steel and AR500 in the various combinations tested may be appliedand secured to any portion of the tank 20 requiring protection fromballistic impact.

In one embodiment, the steel frame 52 is provided as a valve shield thatis removeably engaged with an output thread of the respective valve 30,39 or bolted on using the same bolt as the valve itself. The frame 52has ballistic-hardened plates secured to each side of the frame 52. Atleast one side of the frame 52 has threads to engage with the threadedportion of the respective valve 30, 39. In addition to protecting therespective valve from projectiles, the frame 52 may also hide the valvefrom view. In one embodiment, the inductive device 10 is designed withall the valves brought to a single location on the tank 20 with a commonframe 52 surrounding the valves that is welded or bolted to the tank 20.

With reference now to FIG. 7a , a removable shield 78 may be placed overthe oil and pressure level gauge 24 as well as any other gauge,thermometer, or analyzer provided with the inductive device 10. Theremovable shield is formed of the same material and has the coatingapplied as previously mentioned for the conservator shield 48.

All of the instruments, gauges, radiator 22 banks and various valves,may be placed in a single location on the inductive device 10 forprotection by a removable shield 78 in a central location. Theinstruments, thermometers and gauges are embodied as devices thatprovide remote-reading capability (meaning remote from the inductivedevice or substation location), such as at the network control center,service personnel mobile devices, and/or the control cabinet 28. The oillevel 24 indicator is also positioned at an angle near ground level sothat the gauge 24 may be read from the ground level as opposed totypical positioning on a side wall of the tank 20 near the cover and notat an angle. A reading panel 80 may also be provided so that the readingof the gauge 24 is visible on the panel 80.

FIGS. 7b, 7c, and 7d show the assembly of the components of the shield78. FIG. 7b shows the mounting brackets 77 welded to the bottom of theconservator 46 on opposing sides of the oil level gauge 24. FIG. 7cdepicts one of the two metal panels 75 that are secured by fasteners tothe brackets 77. The metal panels 75 are formed of AR500 steel welded at45 degree angle. The final assembly of the shield 78 is shown in FIG. 7d, showing that the oil level gauge 24 is protected from view as well asballistic impact.

Other hardening features such as localized barriers 120, 122, 124 asshown in FIGS. 12a and 12b may be constructed around accessories such asvalves and tap change motor drives, respectively, or any otherprojections from the surface of the inductive device tank walls. Thebarriers 120, 122, 124 are formed of hardened steel plates 126 whichsurround the accessory. Depending on the level of protection required,the steel plates are hardened in accordance with materials andthicknesses listed in Tables 9, 10, or 11 depending on the inductivedevice application. Examples of other accessories that may be protectedin this manner include but are not limited to: the conservator, Buchholzrelay, fill valve, CT terminal blocks, dehydrating breather, load tapchanger, control cabinet with gauges, nitrogen bottle cabinet, drainvalve, raw vibration sensors, RMS sensors and manhole covers.

The localized barriers 120, 122, 124 are disassembled by unbolting theprotective plates, or unbolting one side and opening a barrier door 128if present to provide the user access to the accessory for maintenanceand instrument reading. When designing the hardened plates to be removedby the user, the manual handling weight of each removable plate is under23 kilograms.

Exterior accessories can be protected using a common barrier designhaving hardened plates applied to frames that can be welded directly tothe tank wall, cover, or any suitable surface. The hardened plates arebolted to the frame to provide protection. For access to smallerdevices, the front barrier can be removed. For small and largeaccessories, the front barrier can be designed with hinges to create adoor as shown in FIG. 12 b.

The shape of the barrier will be determined by the location of theaccessory. For example, FIGS. 10a and 10b depict barriers that aremounted on the tank wall 23 and have three sides exposed, however, anaccessory mounted on the top wall of the inductive device 10 wouldrequire protection from all four sides.

With reference now to FIG. 44, an inductive device 10 having removableand sliding ballistic-resistant panels 42, 44 for protecting the controlcabinet 28 is shown. It should be understood that a tap changer may beprovided within the control cabinet 28 or in a separate cabinet andutilizes the removable and sliding ballistic-resistant panels 42, 44 forprotection. Typical control cabinets 28 are provided with glass windowsfor viewing the electronic equipment inside the control cabinets 28.Therefore, the removable and sliding ballistic-resistant panels 42, 44provide protection to otherwise exposed parts of the control cabinet 28.

The inductive device tank 20 in FIG. 44 is formed of armor or mild steeland the coating in the thicknesses mentioned above, if provided as a newtransformer. New inductive devices 10 having mild or armor steel tanks20 may be provided with meters and indicators installed outside the tank20 for simplified reading access, however, the electronics of thecontrol cabinet 28 are protected by the AR500 steel and/or coatingapplied to the outer surface of the control cabinet 28.

For new and retrofit inductive devices, the tank 20 is formed of a armoror mild steel and has the coating applied to the outer surfaces of thetank 20. Alternatively, the tank 20 is formed of mild steel andenveloped with a blanket or coating of a triaxial aromatic aramideformed of fibers such as polyester, polyamide, or aromatic aramide, asis sold under the trademark KEVLAR®, a registered trademark of E. I. DuPont De Nemours and Company. In particular, the triaxial aromaticaramide fabric is formed of p-aramid fibers based on poly(p-phenyleneterephthalamide). In one embodiment, the conservator 48 may also bewrapped a fabric or provided with an outer coating of a triaxialaromatic aramide.

New and retrofit inductive devices 10, are provided with fixed,removable, and/or sliding door ballistic panels 42, 44 that are formedof AR 500 steel. In one embodiment, the fixed, removable, and/or slidingdoor ballistic panels 42, 44 are provided with a steel plate having aspecial shape or composition that is engineered to deflect or ricochetthe ballistic projectiles from the contact surface.

With reference now to FIG. 45, a radiator shield 70 is provided. Theradiator shield 70 is removable and spaced apart from the front of thebank of radiators 22 for a dual purpose of protecting the radiators fromprojectiles as well as preventing the cooling air from escaping byforcing air circulation. The shield may be formed of a single sheet ofmetal such as armor steel or plates of armor steel that are weldedtogether to form a multi-wall structure.

In one embodiment, the metal sheet or plates of the radiator shield 70are formed of corrugated 14-gauge or 16-gauge steel. In that sameembodiment, the radiator shield 70 protects the inductive device 10 fromlow angle high velocity fragments, shrapnel, and improvised explosivedevices while offering protection as an anti-ram vehicle barrier. Theradiator shield 70 may be designed as a bin to be filled with sand tofurther bolster the radiator shield 70 against incoming intrusions.

In one embodiment, a blanket of or triaxial aromatic aramide fabric isplaced over the radiator shield 70 as a curtain to provide an extralayer of protection. Locating the radiators 22 and the back-up watercooling system in the same bank and protecting the entire bank by aradiator shield 70, centralizes the bank and allows for a singleradiator shield 70 for ballistic protection.

With reference now to FIG. 46, the inductive device 10 is covered by ablanket 62 formed of a triaxial aromatic aramide fabric formed of fiberssuch as polyester, polyamide, or aromatic aramide. The blanket 62 islocated on the low-voltage side of the inductive device 10 so as toprotect the bushings 12, 14 and the conservator 46. In one embodiment,supports 48 may be provided on each end of the transformer tank with arod connecting between the two supports so that the blanket 62 can beplaced over the rod like a tarp. Alternatively, the ballistic-resistantblanket 62, is wrapped around the tank 20 and/or conservator 46 andsecured using tie-wrapping or fasteners. The ballistic-resistant blanket62 protects the transformer and also serves to hide potential targets onthe inductive device 10.

The blanket 62 along with the coating applied to outer surfaces of thebushings 12, 14 and conservator 46, provides a double layer ofprotection in case the projectile punctures the blanket 62 and contactsthe surface of the bushings 12, 14 and/or conservator 46. Additionally,the ballistic-resistant blanket 62 protects other devices provided onthe cover of the inductive device 10.

A rapid pressure rise relay is also provided and detects sudden changesto the pressure experienced by the tank 20. The rapid pressure riserelay works in conjunction with a pressure relief device to release thepressure until an acceptable level is achieved. The pressure reliefdevice automatically reseals upon the rapid pressure rise relaydetecting an acceptable operating pressure level. The pressure reliefdevice is integrated with the oil drain pipe 39 to direct oil to theground.

With reference now to FIG. 47, the inductive device 10 is shown havingwall shields 72 to brace weaker portions of the wall and/or stiffeners54. A ballistic resistant material such as sand may be placed inside thestiffeners 54 in order to protect the tank 20 and active part. The wallshields 72 are used to protect the side walls and any accessories,gauges and valves mounted thereon. Sand bags may also be attached to thetank 20 or cover so that the bags cover the surface of the tank 20corresponding to the active part or other components of the inductivedevice 10, that when compromised may cause damage to the active part.

In one embodiment, the entire transformer 10 and all peripherals arecompletely surrounded by a concrete wall 76 or ballistic-resistantblanket 62 as depicted in FIGS. 48 and 49.

With reference now to FIGS. 8a and 8b , resilient cooling protection forthe inductive device in the form of OFAF (forced oil/forced air heatexchanger coolers) tank mounted coolers 92 is shown. Ballistic plates 92are secured around the vertical sides of OFAF coolers except over thefans 94, so that all vertical edges and surfaces are protected by theballistic plates. The OFAF coolers are designed to direct air verticallyusing the fans 94. The placement of the ballistic plates 92 does notobstruct the air flow of the fans 94 of the OFAF coolers 92 as shown inFIG. 8 b.

The plates 92 for protecting the coolers 90 are attached to framesfurther mounted to the tank via studs or welds. The sides of the coolers90 with the air inlet or outlet must not be covered or coolinginefficiency results. In addition to protecting the coolers 90 from theimpact of a projectile, the ballistic plates are used to protect theedge of the coolers 90 that is in the bullet line of sight as well ascamouflage the coolers 90.

The plates 92 are formed of the metal and/or coating as previouslydescribed for the conservator shield 48 and other inductive devicecomponents protected by ballistic plates 92. The advantage of using OFAFheat exchangers is that the size and weight is only 25% of equivalentradiator/fan cooling.

Ballistic-hardened plates 92 may be retrofit to the side of the radiator22 or ONAF cooler 90 edges to prevent bullet penetration of ONAF coolingequipment (radiators with fans). In one embodiment, the cooling systemhas a radiator 22 or ONAF cooler 90 proximate to each of two opposingside walls 23 of the inductive device tank as shown in FIG. 8a and onlythe opposing side walls of the radiators 22 or ONAF coolers 90 arefitted with plates 92 so that the fans 94 are not obstructed.

Each radiator 22 or ONAF cooler 90 has a top wall, a bottom wall andside walls and at least one fan 94. A plate 92 is attached to each ofopposing side walls of the cooling system and the coating is bonded toouter substrate surfaces of the plates. ONAF cooling equipment may beretrofit with ballistic plates 92 in the same manner as the OFAFcoolers. Additional or larger fans may be needed to compensate for anyreduction in cooling capacity due to the installation of the ballisticprotection plates 92.

The ballistic plates 92 are hung off of tank-mounted frames and areeither AR500 steel or lighter weight mild steel with a ballistic coatingwith thicknesses and coatings as described above in the test results andfor other ballistic plates installed with the inductive device 10.

Cooling is vital to an inductive device and an inductive device can onlyoperate for a short time with damaged or reduced cooling. The desiredoutcome for cooling resiliency during a ballistic event would be totalprevention with no loss of service (ballistic does not penetrate theinductive device and there is secondary cooling that comes online).Alternatively, the inductive device failure prevention by forced shutdown with optional pre-planned cooling replacement is utilized tominimize the outage time.

Bullet penetration of an inductive device is detected by a rapid drop inoil level that is not consistent with load or ambient temperaturechange. The detection is achieved with an electronic oil level sensor. Adata acquisition unit 106 having a processor 108 and non-transitorycomputer readable storage medium 110 having thereon a plurality ofmachine-readable instructions 112 that when executed by at least onecomputer processor 108 cause the at least one computer processor 108 tocompare at least one of temperature, oil pressure and oil levelmeasurements against predetermined thresholds for at least one of themeasured values to determine whether the measurement is actionable.

A comparison of the inductive device load and ambient temperature toexpected values for load and ambient temperature is used to determinewhether the measurement is actionable due to a ballistic event or otherevent. If it is determined that the measurement is actionable, theinductive device is immediately tripped offline to prevent metalcontamination from the ballistic event causing dielectric failure of theinductive device. Thus, the integrity of the inductive device core/coilsis saved, however, there could be significant loss of oil (environmentalevent) and significant repair costs.

Inductive devices with conservators 46 normally have a minimum oil leveldetection in the conservator piping that eventually alarms and/or tripsthe inductive device. A combined oil level and pressure sensor canrapidly detect rapid pressure drop and notify the control center of oillevel and/or pressure below a pre-determined threshold.

In the event of a pressure or oil level drop below the threshold, therepair work may include tank repair, cooling replacement in the eventthat coolers 90, 96 were bullet penetrated, internal inspection of thetank for contamination by spall or other impact-generated fragments,providing new oil and vacuum filling. Mobile coolers 96 could also beused to keep the unit in operation at a reduced oil and pressure levelif new cooling must be supplied as depicted in FIG. 9. The mobilecoolers 96 have supports 98 that allow for placement of the coolers 90next to the inductive device 10.

The cooling valves are triggered by the data acquisition unit 106 toimmediately close in order to further prevent metal contamination fromentering the windings and to limit the loss of oil. Therefore, if abullet penetrated the coolers 90, the loss of oil would be limited tothe cooling oil volume only.

To apply a resilient cooling solution to existing inductive devices,electrically actuated cooling valves are provided. The electricallyactuated cooling valves are installed by closing the present valves (ateach cooler or in the cooler piping for remote cooling), draining thecooling oil to the conservator, removing all cooling equipment,installing new electrically actuated cooling valves next to the existingvalves, reinstalling the cooling equipment and refilling with coolingoil (optionally, pulling vacuum while refilling with cooling oil couldbe performed). The outage time may be 1-3 days or just a matter of hoursif a vacuum is used. Further, in the event of detection of a ballisticevent, the data acquisition unit 106 causes the primary cooling to beclosed and removed from the inductive device oil flow. Concurrently, thedata acquisition unit 106 triggers the secondary cooling to enteroperation.

Examples of electrically actuated cooling valves that may be used withthe present disclosure are ABZ high performance butterfly valvesavailable from Forum Energy Technologies of Houston, Tex.

With reference now to table 12 the aforementioned cooling options aresummarized.

TABLE 12 Loss of Service Time (if ballistic Option event) CommentBallistic Event Sensor and Weeks Only prevents Transformer Shut Downtransformer Failure Automated Valve Shut Off Weeks Only preventstransformer Failure Replacement Radiators 1-2 days Only preventstransformer Failure Retrofit ONAF cooling with Zero Total Protection -ballistic protection plate no loss of service Retrofit OFAF cooling withZero Total Protection - ballistic protection plates no loss of serviceReplace existing cooling with Zero Total Protection - new ABB designedballistic no loss of service secure OFAF coolers Install secondarycooling Zero Total Protection - no loss of service

With reference now to FIG. 43, a shut-down sequence for protecting theactive part of the inductive device 10 is depicted. The shut-downsequence is activated when a drop in oil pressure and/or oil level isdetected at or above a predetermined threshold, such as may occur whenthe inductive device 10 is struck by an object such as a projectile thatcauses loss of dielectric fluid. In normal operation, a radiator coolingsystem 22 having an upper radiator valve 34, a lower radiator valve 36,and fans 18 cools the inductive device 10 during operation, and oillevel and pressure gauges 24 work in conjunction with the back-up watercooling system 33 to cool the inductive device 10. In the case of thecooling radiators becoming punctured by projectile, such as a bullet,the oil level and pressure gauge 24 detects the drop in oil pressure andenacts a sequence of valve actuations as described in FIG. 43. Inparticular, the sequence is designed to protect the active part of thetransformer 10 from being damaged.

The valve sequences are designed to isolate the damaged radiator 22cooling sections and transfer cooling operations to the back-up watercooling system 33. First, the combined oil level and pressure gauge 24,at step 1, detects and provides a quick response to changes ininsulating fluid pressure and level caused by radiator panels beingpunctured and leaking insulating fluid. Next, at steps 2 and 3, theupper radiator valve 34 and lower radiator valve 36, both valves 34, 36having an actuator, simultaneously close when a signal is sent from theoil level and pressure gauge 24 upon critical low oil level detection,such as below a lower limit value for oil level.

After the upper and lower radiator values 34, 36 are closed, at step 4as indicated in FIG. 2, the water cooling back-up system 33 thatincludes a pump, is actuated when a signal is sent from the oil leveland pressure gauge 24 upon critical low oil level detection by the oillevel gauge. The back-up water cooling system is connected to a standardwater supply and continually draws water into the cooling system of thetransformer 10. Alternatively, the back-up water cooling system is areservoir or tank containing water that is pumped into the transformer10 to cool the insulating fluid. The water cooling back-up system 33 andpump are housed in a container for protection against ballisticprojectiles and other intrusions.

The inductive device 10 is equipped with vibration sensors for sensingimpact and an alarm for notifying personnel when the transformer 10receives a shock or vibration, such as from a ballistic projectile. Ifthe shock, vibration or noise level is above the threshold for shocks orvibrations experienced during normal operation of the inductive device10, a safety mode is activated. The safety mode that is enacted when thetransformer receives an impact such as a shock as a ballistic projectileor an acoustic signal above the predetermined threshold is measuredhalts the tap changer mechanism and starts all of the fans in case ofradiator 22 shut down. The sequential safe shutdown of the transformermay occur, for example, upon opening of the pressure relief valve 30. Inthis case, the power interruption device such as circuit breakersprotecting the inductive device 10 have contacts opened by a relay incommunication with the valve 30 and/or the oil level and pressure gauge24. Alternatively, the back-up water cooler system 33 is activated inthe case of radiator 22 shut down.

With reference now to FIGS. 10-11 and table 13 below, a series of testswere performed by the inventors to determine the effect of the appliedcoating on the noise level of the inductive device. The tests wereconducted in accordance with the IEEE C57.12.90 2010 “Standard test codefor liquid-immersed distribution, power and regulating transformers”using the 69 kV, 12/16/20 MVA transformer that was coated with XS-350 inthe manner previously described. It was found that the noise level ofthe transformer during the test was reduced by at least 4 decibels incomparison to a non-coated transformer of identical construction.

The noise measurement performed on the coated and un-coated transformerswas a total core noise measurement test. The comparison of the totalcore noise tests is provided below in table 13:

TABLE 13 Audible Noise Measurement (Coated vs. Uncoated TransformerTank) Core Core noise, Effect of noise, dB dB coating, Frequency(reference) (w/coating) dB Total 65 60.7 −4.3

The analysis of the noise data shows a maximum of a 4.3 dB reduction ofthe total core noise level for the inductive device with the coating incomparison to an inductive device without the coating. Therefore, theinductive device having the coating applied thereto has from about a 0.1dB to about a 4.3 dB reduction in core noise level as compared to anuncoated inductive device. The inductive device used in the noise leveltest series had a tank formed of ASTM A36 mild steel having a ⅜ inchthickness. Additionally, the XS-350 was applied to the tank side walls23 at a ½ inch thickness.

With reference now to FIG. 10, measurements were taken at 26 measurementpoints using 26 acoustic sensors surrounding the inductive device coatedwith XS-350. Each acoustic sensor was mounted on a stand at a height of⅓ or ⅔ of the inductive device tank total height (Ht in FIG. 10) fromthe base of the tank or ground level. Sound pressure level measurements,L_(i), at the indicated frequencies of 12.5 to 2,000 Hertz were recordedin FIG. 10.

The energy average inductive device sound pressure level is calculatedby averaging the ambient-corrected sound pressure levels measured ateach microphone (acoustic sensor) location and for each frequency band(A-weighted, one-third octave band, or discrete frequency) usingEquation (34):

$L_{p} = {10 \times \log_{10}\left\{ {\frac{1}{N}{\sum\limits_{i = 1}^{N}{10\left( \frac{Li}{10} \right)}}} \right\}}$

Wherein:

L_(i) is the sound pressure level measured at the ith location for theA-weighted sound level, for a one-third octave frequency band, or for adiscrete frequency (dB); and

N is the total number of sound measurements.

The arithmetic mean of the measured sound pressure levels may be used todetermine the average inductive device sound pressure level when thevariation of the measured levels is 3 dB or less or when an approximatevalue of the average inductive device sound level is desired.

The first column of FIG. 11 entitled “AVG” is the average of

$10\bigwedge\left( \frac{Li}{10} \right)$of all measurements for the frequency in the column entitled “Freq.” The“L_(p)” column provides the values for 10*log(AVG). L_(p) is equal to60.67 for the test of the coated inductive device described above. Ascompared to the test results for the uncoated inductive device measuring65 dB core noise, the coated inductive device experienced a reduction inthe total core noise level of 4.3 dB.

It should be understood that various factors impact core noise levelmeasurements including but not limited to: design and construction ofthe core, coil, and tank and measurement accuracy of the noise levelmeasuring system. Due to these factors, it is expected that a total corenoise level reduction above 4.3 dB may be achieved.

The XS-350 polyurea coating was tested for environmental integrity asoutdoor applications expose the inductive device housing to factors suchas pollution, rain, snow, wind, dust, and ultraviolet rays that maydegrade the coating over time. In particular, humidity, ultravioletaccelerated weathering (QUV), and simulated corrosive atmosphericbreakdown (SCAB) tests were performed. The humidity test performed inaccordance with ASTM standard D3363-11 was conducted using 2 test panelshaving the coating applied thereto. The test panels were evaluated forblistering and softening and were found to meet the ASTM standardD3363-11 specification.

The ultraviolet accelerated weathering test (QUV) was performed inaccordance with the ASTM standard D523-14 and the gloss of the coatingwas evaluated prior to and after the test. The test panels met the ASTMstandard D523-14 specification. A visual test evaluation of cracking andcrazing of the QUV samples met the specification as well.

The simulated corrosive atmospheric breaks (SCAB) testing was performedin accordance IEEE standard C57.12.28-2014 for 504 hours of UV exposure,scribe, and fifteen exposure cycles over three weeks for sections athrough d. All of the tests met the specification in accordance withIEEE standard C57.12.28-2014.

Ballistic Impact Sensing

Inductive devices such as large power transformers are crucial powersystem components for reliable transmission and distribution of bulkpower to end-users. A transformer failure due to a deliberate damage ortampering is a significant event that can lead to a major outage orcause a blackout. The design and manufacture cycle for large powertransformers can take at least a year or longer. Often times, theconsequential damages resulting from loss of a substation transformercan exceed the transformer replacement cost and therefore securingtransformers in transmission and distribution substations is a NERC CIP(Critical Infrastructure Protection) requirement.

A transformer having its physical integrity compromised needs to bedealt with immediately to contain the magnitude of the damage and avoidsubstantial consequential losses as a result of inductive device failureincluding a potential blackout. A sensor-based solution developed by theinventors and disclosed herein continuously assesses the physicalsecurity of a an inductive device such as a substation transformer andalarms the operators in time to take corrective and/or preventivemeasures in the event of an attack that would compromise the integrityof the operation of the inductive device. Corrective measures areinitiated when the determination is made that the inductive devicesuffered sustained damage. Preventive measures may be initiated in caseswhere no immediate damage is suspected but the goal is to prevent futureincidents and reduce the likelihood of an incipient failure.

The sensor-based solution detects and responds to possible attacks onsubstation inductive devices and other electrical equipment as well asprovides automated damage assessment and awareness to utility controlcenter 130 personnel and other operators.

Tests were carried out using data to represent potential events,dangerous or not, including gunshots, thrown rocks, and hammer strikes.A system and a method to detect impact to a stationary inductive devicesuch as a transformer (or other electrical equipment) and discernbetween impact of a bullet to the inductive device tank 20,characterized as an attack on a inductive device, and a non-bulletstrike is provided.

A high level embodiment of the sensor-based electrical equipmentphysical security system is shown in FIG. 13. The major components ofthe system include various sensors 102, 104, a sensor data processingunit 106, a remote terminal unit (RTU) 132 for remote communications,and an interface to a control center 130. The sensors may be wired,wireless, or autonomous sensors with power harvesting features requiringno power source for operation. The sensors measure various physicalquantities related to motion, sound, light intensity, and otherenvironmental factors. For example, the sensors may measure accelerationalong three axes and sound waves.

The sensors may be installed stand-alone around the inductive device,attached to the inductive device tank 20, or installed inside the tank.The data from these sensors are gathered by the sensor data processingunit 106. The processor receives the sensor data and time-stamps therecords. The sensor data processing unit 106 further performspreliminary data processing tasks such as filtering and averaging on theraw data. In one embodiment, the sensor data processing unit 106 alsoruns detection algorithms for local alarming and annunciation. Theoutput from the sensor data processing unit 106 is received by the RTU132 and communicated over a preferred communications medium to theutility control center 130 interface system.

In one embodiment, the interface system may receive the data from theRTUs and run algorithms on the data set for damage assessment and adetailed integrity check. The final outcome is displayed on the operatordashboard in real-time to allow actions to be taken. In anotherembodiment, the output from the sensors is used to control the closingof cooling system valves in the event of loss of oil detected by othermeans. In that same embodiment, the output from the sensors is also usedto open valves to enable the application of a redundant cooling systemfor the inductive device.

The sensor system is used as a trigger system primarily for activatingother security systems, such as substation monitoring and surveillancesystems 136. For example, it can be used to guide the cameras to takespecific shots of the inductive device or substation perimeters. Suchevidence gathered just-in-time may be used for forensic analysis.

In this case, the data processing unit runs a set of algorithms todetermine the onset of an impact and sends a trigger signal to theappropriate monitoring and surveillance systems for detailed measurementand recording of the impact event. The surveillance system is flexibleenough to detect an impact just before and as the impact is occurring asopposed to prior art systems that utilize surveillance equipment (ie.cameras) fixed at particular angles and assets or moving with slow speedand likely to miss the onset of the attack.

With reference now to FIG. 14, the steps for detecting an impact andtaking action on the detected impact are provided. The steps may beimplemented in the data processing unit 106 or in control center 130computers with varying levels of complexity.

At step 138, the sensor data is received. The sensor data is thenbuffered and pre-processed at step 140. Pre-processing prepares andcleanses the data for analysis in the subsequent steps. The typicalfunctions covered by pre-processing may include removing noise from themeasurements, filtering/re-sampling, segmentation, and/or aggregation.Filtering removes the unwanted components from the measurements.Segmentation returns the period of interest in a data set andaggregation is a technique that combines data from multiple sources orprovides uniformity to the disparate data that arrive at different timeintervals.

At step 142, informative characteristics are extracted which may be inthe time, frequency, or time-frequency domain. The characteristics arefed to a classifier at step 144 that assigns a label for the data setwhich in turn is used for a logic check at step 146. Depending on theresult of the detection logic, the flow either returns to the nextinterval of data processing at step 138 or is transferred to the alarmblock at step 148, triggering further actions by the operator or by asubstation surveillance system.

The data generated by a series of trials conducted by the inventorssuggest the ability to differentiate between the gunshot and non-gunshotusing signal waveform characteristics such as the presence of theshockwave signal from the supersonic bullets as well as the signal fromthe muzzle blast. However, it is important to note that not all gunshotswill have these characteristics, as some gunshots are subsonic, themuzzle blast signal may be limited with a suppressor and there may bephysical interference between the blast and the sensor. Although notidentical, the acceleration response of the strongest hammer strike issimilar to that of some of the gunshots. Different waveformcharacteristics could be used to identify gunshot and non-gunshotimpacts.

For instance, a supersonic projectile has two forms of acoustic energy,shockwave and muzzle blast. The shockwave occurs before the muzzle blastin time as is shown in FIG. 21. The shockwave and muzzle blast areunique to firearms, therefore, it is clear that a bullet has beendischarged from a firearm.

A schematic of a system 100 for detecting impacts to inductive devicesand other equipment at a substation is shown in FIG. 15. The system 100has at least one acoustic sensor 104, at least one vibrationsensor/accelerometer 102, and the data acquisition unit 106 having aprocessor 108 and non-transitory computer readable storage medium 110having thereon a plurality of machine-readable instructions 112 thatwhen executed by at least one computer processor 108 cause the at leastone computer processor 108 to compare signals received from the acoustic104 and vibration sensors 102 against thresholds for sound pressure andacceleration to determine whether the impact is from an object such as agunshot projectile or a non-gunshot projectile. As a minimum, oneaccelerometer may be required to detect impact whether gunshot relatedor not. Further, if either of the measured sound pressure andacceleration values exceed the predetermined thresholds, an alarm issent to the operator or utility control center. Additionally, if eitherof the measured sound pressure and acceleration values exceed or meetpredetermined thresholds in conjunction with an increase in oiltemperature or drop in oil pressure or oil level. The sound pressure andacceleration data is recorded in the database of the data acquisitionunit and/or computer at the network control center.

If it is determined that the impact is due to a gunshot projectile,various actions can be taken such as directing a surveillance camera atthe substation to the inductive device that has been struck or is in thepath of the projectile and the vicinity around the inductive device.When the location of the shooter can be determined based on sensor datadescribed below, the surveillance camera may be directed toward theshooter's location and a facial recognition sequence may be initiated.Further, backup cooling sequences may be initiated for the inductivedevice when it is determined that the inductive device is under attackand valves may be closed to prevent the leakage of dielectric fluid fromthe inductive device.

The at least one vibration sensor and at least one acoustic sensor areeach wired to the data acquisition unit. The at least one vibrationsensor is in contact with the inductive device tank 20 and the at leastone acoustic sensor is positioned in or out of contact with theinductive device tank 20. It should be understood that more than onesensor of each type may be used in various combinations depending uponthe desired results as indicated in Table 15 which will be described inmore detail later.

During the series of sensor-based ballistic tests, the shooter lined upapproximately 60 meters away from and orthogonal to the tank 20. Testswere performed on an inductive device tank 20 that was filled to abouttwo-thirds of its height with water and was coated with ½ inch of theXS-350 coating prior to the testing.

With reference now to FIG. 16, the vibration sensors were attachedproximate to the bottom of the tank wall. The acoustic sensor wasapproximately 1 meter closer to the shooter than the rest of thesensors, as it was attached to the edge of the platform 150.

During the test trials described in Table 14, data was collected fromfour sensors including two raw vibration sensors, one RMS accelerometerand one acoustic sensor. The RMS accelerometer is a wired accelerometerand has a measurement range of from 0.0 to 10 g rms, an output of 4-20mA, and a frequency range (+−3 dB) from 180 cycles per minute to 600000cycles per minute (cpm). The sensor mounting positions are shown in FIG.8 from left to right, and the far right sensor, RV2, is closest to theshooter.

Twelve shots were fired using the various guns and ammunition at thepoints indicated in relation to the water line shown in FIG. 17. Thewater line is meant to represent the fluid level of dielectric fluideven though water was used in the testing.

TABLE 14 Test parameters for each test run Case # Bullet Information 1223; 55 grain; FMJ 2 223; 55 grain; FMJ 3 223A; 55 grain; FMJ 4 270; 140grain; ballistic tip 5 308, 167 grain; FMJ 6 30-06; 150 grain; core locktip 7 300 WBY MAG; 150 grain; InterBond ballistic tip 8 300 WBY MAG; 180grain; SpirePoint soft lead tip 9 300 WBY MAG; 180 grain; SpirePointsoft lead tip 10 325 WSM; 200 grain; red AccuBond tip 11 270; 140 grain;ballistic tip 12 270; 140 grain; ballistic tip

With reference now to FIG. 17, the bullet contact points on theinductive device façade are shown and the bullets are numbered inaccordance with the Table 14 test trials. All trials except for testtrial 11 were above the center line of the tank 20.

Four impact tests were conducted in addition to the twelve test trialspreviously mentioned and were administered to the right-facing wall ofthe tank 20. Of the additional four tests, two recorded the impact of arock, and two recorded the impact of a hammer.

With reference now to FIG. 18, the gunshot vibration response inacceleration vs. time as measured by the first and second raw vibrationsensors as well as the RMS sensor is shown for the .270 caliber (140grain) ammunition having a ballistic tip as was tested in trial 4. Trial4 is used as an example for different impact scenarios in relation toFIGS. 18, 19, 21, and 22.

The bullet from trial 4 was closer to the location of RV1 than RV2.Thus, RV1 processed the impact and vibration first. The negativeacceleration recoil is delayed for RV1 in FIG. 18 whereas the negativeacceleration recoil is continuous for RV2.

With reference now to FIG. 19, the acoustic response of the gunshot oftrial 4 is depicted. The acoustic sensor measures in Pascals and theconversion to decibels is based on a reference pressure that representsthe lowest audible noise. In air, the reference pressure correspondingto the lowest audible noise is about 20 μPa. The equation to convertbetween decibels and Pascals is:

$\lbrack{dB}\rbrack = {10{{\log_{10}\left( \left\lbrack \frac{({Pa}\rbrack}{P_{ref}} \right\rbrack^{2} \right)}.}}$The conversion chart for Pascals to decibels is shown in FIG. 20.

With reference now to FIG. 21, the shockwave and muzzle blast for trial4 is depicted. The shockwave from the bullet occurs just after 2.82seconds. The muzzle blast occurs just before 2.92 seconds. The shockwaveand muzzle blast both travel at the speed of sound. The part of theshockwave that is recorded by the acoustic sensor is not created untilthe bullet is approaching the tank 20. The muzzle blast has a head startin terms of the moment of launch and the supersonic bullet makes up forthe time delay by the short distance the shockwave has to travel.Approximate calculations also predicted a time difference between themuzzle blast and shockwave of almost exactly 0.1 seconds.

With continued reference to FIG. 21, the amplitude of the peaks isimportant to consider. While the shockwave appears to create a largerpeak-to-peak pressure, this is not actually the case. Sound pressure isinversely proportional to distance traveled, and the muzzle blastoccurred about 60 m away, while the shockwave was much closer. Adjustingfor distance, the amplitude of the muzzle blast (defined by half thespan of the peak-to-peak) would be 178 dB at 1 meter away from theshooter, as opposed to the unadjusted 143 dB. Likewise, the adjustedshockwave level is 161 dB instead of 150 dB. For scale, a normal voiceconversation occurs around 60 dB. Based on a logarithmic scale, thiscorresponds to 0.02 Pa. Conservative estimates were made for thesaturated portion of the shockwave signal.

The durations of the signals were analyzed using an approximate formulaprovided below to calculate the theoretical time interval of theshockwave based on bullet size and speed:

$T \approx {1.82\left( \frac{d}{c} \right)\left( \frac{Mx}{l} \right)^{\frac{1}{4}}}$

Here, d is the bullet diameter, l is the bullet length, c is the speedof sound, M is the Mach number (bullet velocity/c), and x is thedistance between the bullet's trajectory and the microphone at the pointof closest approach. This yielded a time of approximately 0.16milliseconds, while the graphical peak-to-peak time is approximately0.098 milliseconds. No other signal is on this time order of magnitudeas is the muzzle blast duration of approximately 2 milliseconds.

With reference now to FIG. 22, and zooming in on the white spaceimmediately after the first event occurring at 2.823 seconds, a cleansignal representing the shockwave is present. However, at 2.825 seconds,the signal's calm decay turns rampant with multiple oscillations. Thisis explained by the sound from the impact, which was also calculated tooccur two milliseconds after the shockwave signal arrived. The manyoscillations of the shockwave signal likely come from different pathsthe sound from impact could have taken to the sensor, specificallyreflections off the platform 150.

Referring now to FIGS. 23-26, rock and hammer trials were performed anddata was collected from these trials. The rock trials had far fewercomponents than the gunshot trials. The first component is theacceleration from Rock Trial 1 in FIG. 23. It is important to note thatthe rock was thrown at the right face of the tank, so the signal fromRV2 greatly dominates the signal from RV1. RV2 reaches saturationdespite the much lower force. However, there are clear differences inthe RMS sensor, which has a much slower rise and lower maximum value.The RV signals are also much more oscillatory and stay centered on thex-axis than those of the gunshots, although this may in part be due tothe location of contact. These observations support the usage ofwaveform characteristics to differentiate between gunshot events fromnon-gunshot events.

With reference now to FIG. 24, the acoustic signal of the rock throwoffers more difference as the magnitude is significantly lower than thatof a gunshot and there is no signature waveform of any kind. Theacoustic rock throw signal tends to the negative pressure side, althoughnot as much as the gunshot data.

A first hammer trial was conducted and proved as unimpressive as therock throws. However, the second hammer trial was more forceful and isdepicted in FIG. 25. The raw vibration sensors had very similar hammerstrike temporal profiles to that of the gunshots, and the RMS takes asimilar shape for the hammer strikes as the gunshot. While the maximumRMS value here is less than the lowest for the gunshots, this data setsuggests it would be possible to reach the same RMS value as the lowerend gunshots with just a household hammer. This observation supports theidea that amplitude of the RMS values alone may not be sufficient todifferentiate gunshot events from non-gunshot events. Other waveformcharacteristics in time domain, frequency domain and time-frequencydomain may be used to reduce false alarms such as when a non-gunshotevent is tagged as a gunshot event.

An example of a time domain characteristic is the decay time constant asshown in FIG. 31. FIG. 31 takes the lowest maximum RMS from the bullettrials (^(˜)5.5 g) and compares it to the highest maximum RMS from thenon-bullet trials (^(˜)4.9 g) wherein g is the acceleration due togravity and is expressed in meters/(second)². It should be consideredthat a non-firearm attack, while much less likely to penetrate theinductive device, could still cause damage if at a large enoughmagnitude. This would also signify other issues regarding the physicalsecurity of the substation and should be flagged.

With continued reference to FIG. 31, a line 150 is drawn at 4 gacceleration to depict the difference in the time decay constant of thebullet versus the non-bullet. The non-bullet signal decays faster thanthe bullet signal. For example, point 152 of the non-bullet vibrationsignal occurs at 4 g acceleration and 0.35 seconds after the initialvibration detection. In contrast, point 154 of the bullet vibrationsignal occurs at 4 g acceleration and 0.41 seconds. This means that thevibration data can be used to cross-check the acoustic data forcertainty of a bullet impact to the tank

Referring now to FIG. 26, the acoustic data of hammer trial 2 also hassome similarities to the gunshots. However, the acoustic data of hammertrial 2 has a lower maximum amplitude and a complete lack ofidentifiable events. The signal still trends negative while oscillatingbefore making a positive run, but a closer look shows no single eventthat can be isolated.

The raw vibration sensors RV1 and RV2 saturated quickly, rendering itimpossible to differentiate among bullet calibers based on the maximumvalue of this measurement. FIG. 28 is a graph comparing maximumacceleration to caliber size and in which the rock is treated as acaliber size of 0.35 inches and the hammer is treated as a caliber sizeof 0.40 inches to allow inclusion on the graph. While all gunshots lookthe same in FIG. 28, the rock trials signals only drop lower on thesensor farther from impact. Likewise, the hammer trials see oneoccurrence of the far sensor not saturating, while the other threemeasurements (trial 1 RV2, trial 2 RV2, trial 2 RV1) end up in the samelocation on the graph. For the most part, the data from RV2 plotted overthe data from RV1, as they were in the same location on the graph.

With reference now to FIG. 29, the RMS measurements avoided constantsaturation. However, there does not seem to be a strong correlationbetween caliber size and maximum RMS value.

Referring now to FIG. 30, the acoustic trials showed the pressure waveassociated with a majority of the most impactful strikes at or above 500Pa, while the rock impacts showed pressure levels below 100 Pa.

The defining features separating the gunshots versus the rock and hammerstrikes were the presence of the shockwave and the muzzle blast of thegunshots. While all of the ammunition used in trials 1-12 was notsubsonic, it is not unreasonable that one would actively choose alarger, slower bullet to avoid creating a shockwave. Different signalattributes in time and/or frequency domain may be used to account forthese differences as previously mentioned.

With respect to the muzzle blast, the use of a suppressor needs to beconsidered. While this will make the signal quieter, commercialsuppressors do not make a gunshot quiet, as may be assumed. Rather,commercial suppressors reduce the noise of a gunshot by an average of20-35 dB, which is roughly the same as earplugs or earmuffs.

The bigger concern with the muzzle blast, however, is the “line ofsight” and angle between the blast and the sensor. If there are physicalobstructions between the blast and the sensor, the signal will begreatly decreased. This is also true if the shot is travelling at alarge angle relative to the sensor, although sensor placement near theelectrical equipment of interest should take care of that issue.Additionally, atmospheric conditions have an effect on the speed ofsound and thus, the acoustic signal.

Two categories of possible solutions and systems for sensing a ballisticimpact and determining whether immediate action should be taken toprotect the transformer were developed by the inventors. The firstcategory solution is a system that utilizes one RMS accelerometer andone acoustic sensor and detects large impacts on the transformer via theaccelerometer, while also being able to differentiate between a gunshotand a blunt force attack via the acoustic sensor. The second categorysolution is a more complex system and will be addressed later.

The first category solution will now be described in detail. The RMSsensor was chosen over the raw vibration sensor because theaccelerometer is only contributing to threshold detection so the actualwaveform does not matter. Furthermore, the RMS sensor is an average ofthe vibration signal over a certain predetermined window, whereas theraw vibration sensor yields instantaneous measured values. Acurrent-based output is preferred, as it is typically more robustagainst noise in the substation environment.

By way of non-limiting example, a PLC that may be used with thesolutions outlined in the present disclosure is the AC500 PLC availablefrom the assignee of the present disclosure. The first category solutionalso has a non-transitory computer readable storage medium havingthereon a plurality of machine-readable instructions that when executedby at least one computer processor cause the at least one computerprocessor to perform a method for detecting if there has been asignificant impact to the inductive device tank.

The first category solution for detecting impact to the inductive devicehas: a raw vibration accelerometer, an RMS accelerometer, an acousticsensor, and a programmable logic controller. The programmable logiccontroller has a base module, an analog input (AI) module and adetection and assertion module. The raw vibration accelerometer may havean output of +/−5 volts corresponding to a measurement range from +/−50g. The raw vibration sensor may be a 2-pin MIL-C 5015 electricalconnector. By way of non-limiting example, a raw vibration accelerometerthat may be used is a PCB 662B01, available from PCB Piezotronics ofDepew, N.Y.

The RMS wired accelerometer may have an output of 4-20 mA correspondingto a measurement range from 0 to 10 g. The RMS accelerometer may be a2-pin MIL-C 5015 electrical connector. By way of non-limiting example,an RMS sensor that may be used is PCB 646B02, available from PCBPiezotronics of Depew, N.Y. FIG. 27 depicts an example of the outputs ofthe RMS accelerometer (RMS) and raw vibration accelerometers (RV1 andRV2) as previously described.

The wired acoustic sensor may be a 40PP CPP Free-field QC Microphoneavailable from G.R.A.S. Sound and Vibration A/S of Holte, Denmark, byway of non-limiting example. The wired acoustic sensor may have adynamic range upper limit of at least 135 dB. The wired acoustic sensoris a BNC electrical connector.

The benefit of the accelerometer is that it will detect any contact withthe transformer and create a signal. However, using just the amplitudesignal of the accelerometer may not be adequate to discern between afirearm-based impact and any other impact. This is supported by thetrials, where one hammer strike was able to cause a raw vibration sensorto saturate for a similar amount of time as a typical bullet strike.

The acoustic sensor is much better at distinguishing between a firearmand other types of impacts. It is assumed that different thresholds areset for: 1) any notable event and for 2) an event caused by a gunshot.Confirming a gunshot is usually done by detecting the presence of twounique acoustic signatures of the expulsion of a supersonic bullet,shockwave and muzzle blast, as previously mentioned.

In any case, the acoustic signal from a gunshot consistently had moresound power than the other trials. Thus, an algorithm may be based on amoving average of a small number of consecutive data points thusachieving an RMS system.

The trial data shows that the acoustic signals from a hammer and agunshot are similar with respect to maximum magnitude. Detailedalgorithms can differentiate between a shockwave (0.196 s) and theinitial spike in the hammer signal (0.197 s). However, simple thresholddetection, using just one inequality may be used to determine thedifference between a bullet and non-bullet.

The absolute maximum values for the weakest gunshot and the strongestnon-gunshot are within 9%. However, with the high-magnitude nature ofthe bullet's impact sound (starting at 0.198 s), the firearm-basedattack generates more sound power than the hammer trial. The hammerstrike, meanwhile, experiences the highest magnitudes upon impact andimmediately begins to attenuate.

With much consideration given to the sampling rate, an average-basedthreshold can be proposed as the gunshot is expected to have largerrelative acoustic values, especially over time. FIG. 33 is an example ofthe method using the acoustic signatures of the maximum hammer impactand the minimum gunshot impact plotted in FIG. 32a . FIG. 33 wasgenerated based the moving average of four data points collected by thePLC.

Instantly, the effect of the PLC moving average is visible, withconsiderably higher values for the gunshot for up to three seconds afterthe initial disturbance. Here, by storing and averaging just fourvalues, a clear average-based threshold can be set to differentiatebetween a firearm and blunt attack. Although the graphs are not shownhere, the results were similar when shifting to from 0 to 0.05, 0.1, and0.15 seconds, with a minimum bullet average of 69.85 Pa and a maximumhammer average of 24.94 Pa.

This differentiation could also be achieved by using an acoustic sensorthat delivers an RMS voltage. Once again, an average-based threshold(including RMS) is better than a single point threshold because thealgorithm receives information encompassing a longer period of time. AnRMS sensor preprocesses the information, making single point detectionpossible.

One clear drawback of this method is the possibility that a bullet doesnot hit anything, so no impact sound is generated. Neither the vibrationnor acoustic sensor would flag this event (unless perhaps the PLC caughtthe shockwave or muzzle blast perfectly) despite the importance ofknowing that a shot was fired. This is a situation where an RMS acousticsensor would have the edge as the shockwave or muzzle blast would stillhave an effect on what the PLC reads, as opposed to the PLC completelyskipping over these events when taking isolated snapshots.

An option that can address some of the shortcomings of using only theaccelerometer sensors or only the acoustic sensors would be to includeone of each. While an accelerometer may not always differentiate betweena firearm and a different type of impact, the combination of anaccelerometer and an acoustic sensor may be used to pick up also thepressure levels and identify a bullet impact. While an acoustic sensormight capture events that are not associated with the inductive devicebut are nearby, cross-referencing with the accelerometer can reveal asimultaneous vibration signal received from the inductive device.

In one embodiment, additional accelerometers are utilized in order toprovide each face of the inductive device with a sensor. In that sameembodiment, it can be determined which side was hit, yielding an initialguess as to the inductive device components that may be damaged. Thesensor to which the bullet was closest may be determined by comparingthe relative magnitudes of the RMS accelerometers.

Depending on the specific magnitudes (e.g. if the largest andsecond-largest are close), the location could be narrowed down evenmore, to being somewhere near the corner between these two sensors. Thismethod uses relative signal attenuation to determine the location ofimpact. It is also theoretically possible to use relative time ofarrival or absolute magnitude to determine exact differences in signalpropagation distances.

Sensor placement is important for the accelerometer given the effects ofattenuation as a signal propagates through its host medium. An impact ofa given impulse on one side of the inductive device should register thesame way with the primary sensor as the signal would on any other sideof the inductive device. Thus, if using a single sensor, the sensorshould be placed in the center of the top face of the prism. While thisis a geometric simplification, it provides the closest arrangement tosymmetry for the four side walls that are perpendicular to the ground.

More overall symmetry could be obtained in the four accelerometersolution, by putting a sensor at the center of all faces. This wouldallow for impact side determination and signal attenuation would beminimized as the average travel distance for the vibration to theclosest sensor will be reduced. It is unlikely that symmetry can beachieved between the top face and any of the other faces, but it is alsoexpected that an impact on the top face is least likely. Alternatively,one sensor may be placed on a side face for ease of installation. Thisplacement is possible with the accelerometer since the waves will travelaround the inductive device.

The acoustic sensor may be similarly placed in a symmetry-inducinglocation such as the center of the top wall or cover of the tank 20.Since the axial vibration can cause unwanted noise in the acousticsensor, it may be advantageous to physically isolate the acoustic sensorfrom the inductive device.

The second category solution uses multiple sensors and more complexalgorithms to provide actionable information, such as the shooterdirection and location, as well as bullet trajectory, speed, caliber,and number of shots. When an impact is detected in real-time, an alarmsignal may be transmitted to the control station and a substation'scamera may be then directed to the location of interest.

The sensors need to respond to attacks on all side walls of theinductive device, so the sensors are placed on the top wall, lid orcover of the inductive device to receive signals equally from the facesperpendicular to the ground and their corresponding directions. Thisarrangement may amplify strikes on the top of the inductive device,however, the arrangement provides the most symmetry, allowing for eventhreshold detection from the other walls of the inductive device. Inthis scenario, the acoustic sensor would ideally be physically isolatedfrom the inductive device vibrations, as the vibrations can manifest asunwanted signals in the acoustic data.

Additional accelerometers may also have some benefit. The most obviousis the ability to cover every face of an inductive device with a sensorin order to symmetrize threshold-based flags. While this will allow forshot direction estimation, the use of even more accelerometers may alsoenable exact contact point triangulation. Contact point triangulationuses relative magnitudes and arrival times after the signal haspropagated through the system. In all cases, the raw vibration sensorsand/or acoustic sensors are placed on predetermined location(s) on thetank 20 or electrical equipment enclosure/housing depending on theinstallation as will be described further.

The acoustic- and vibration-based systems are independent, so variousversions can be interchanged depending upon the installation and as ispresented in table 15 below wherein

V=Vibration sensor

RV=Vibration sensor

A=Acoustic sensor

PLC=Programmable Logic Controller

AIO=Analog I/O Adapter, 8 channels

DAQ=Data Acquisition Device and Logic

AI1=Analog Input Module

AI2=Analog Input Module

TABLE 15 Sensors Logic Pros Cons FIRST CATEGORY SOLUTION COMPONENTS VPLC + Al0 Surest method of Hard to differentiate detecting impactbetween firearms and other impacts; signal attenuation makesnon-symmetrical comparisons difficult; installation on top of inductivedevice A PLC + Al0 Likely able to distinguish Likelihood of falsebetween firearms and positives; installation other impacts; almost aboveinductive device certain to detect impact V + A PLC + Al0 In addition toabove: Installation on top of/ eliminates false above inductive devicepositives from A by cross-referencing with V 4V + A PLC + Al0 Inaddition to above: Acoustic sensor likely allows for installation abovetop determination of which of inductive device inductive device face washit, yielding a rough shooting direction; ease of installation forvibration sensors SECOND CATEGORY SOLUTION COMPONENTS V + A DAQ + Al1Improved firearm Installation on top of/ detection using acoustic aboveinductive device signatures; surest method of detecting impact;eliminates false positives from A by cross referencing with V 4A DAQ +Al2 Likely prediction of Still potential for false azimuth andelevation; positives; installation almost certain to possibly abovedistinguish between inductive device firearms and other impacts; almostcertain to detect impact V + 4A DAQ + In addition to above: Installationon top of/ Al1 + eliminates false above inductive device Al2 positivesfrom A by cross-referencing with V V + 8A DAQ + In addition to above:Installation on top of/ Al1 + likely prediction of above inductivedevice 2Al2 range, yielding full shooter location; higher precisionazimuth and elevation; possible prediction of bullet trajectory,velocity, caliber 12RV- DAQ + High likelihood of System likely to 16RV(34)Al2 determining impact differentiate between location, also yieldingfirearms and other rough shooting direction; impacts ease ofinstallation 16A DAQ + Very high precision 4Al2 estimates for azimuth,elevation, range, bullet trajectory, velocity, caliber; ease ofinstallation for acoustic arrays; likely able to develop protectionagainst false positives

It should be understood that the components of the first and secondcategory solutions are provided by way of non-limiting example and thatthe inventors contemplate other combinations and components that may beused in the systems for detecting impact to inductive devices and otherelectrical equipment. Further, each row in Table 15 indicates a separatesolution for the first and second categories and benefits and drawbacksof each solution. By way of non-limiting example, the DAQ may be acDAQ-9132 (Compact DAQ) data acquisition chassis and logic, availablefrom National Instruments Corporation of Austin, Tex.

The DAQ chassis and controllers control the timing, synchronization, anddata transfer between multiple I/O modules and an external or integratedcomputer. A single DAQ chassis or controller can manage multiple timingengines to run several separate hardware-timed I/O tasks at differentsample rates in the same system. The software required for any PC-basedDAQ system consists of a hardware driver and a development environment.Hardware drivers provide communication between the PC and the DAQdevice, allowing software control of the hardware. The driver contains abuilt-in set of rules called an application programming interface (API)that provides the ability to control the hardware from within aprogramming environment. From the programming environment, the data canbe presented and logged, in addition to the generation of tests, alarmsand output waveforms using the data.

An increased sampling rate may be used to gather more granular acousticdata. A tetrahedral array of sensors using three sensors may be providedand then multiplied for improved accuracy (two arrays having a total ofsix sensors or three arrays having a total of nine sensors). Still otherdistributed wireless sensor networks may have nodes wherein each sensoris a node or a sensor array.

As previously described, there is an acoustic signal from the shockwave,the impact sound, the muzzle blast, and any reflections. The shockwaveand muzzle blast are unique to firearm usage, so the presence of eitherguarantees a gun has been used. However, both of these signals can beobstructed by physical objects in between the detach point and thesensor. Possible obstruction is dependent on both individual substationlayouts as well as placement of the sensor.

It is almost certain that the sensor will capture impact noise. However,unlike the shockwave, muzzle blast and impact shown in FIGS. 21 and 22,this noise is not guaranteed to have a specific waveform. For example,there may not be an obvious difference between a gunshot where only theimpact sound is captured and fireworks or a backfiring car. Furthermore,the same issue arises when comparing the former to a gunshot thatricochets off a structural support near the inductive device but causesno actual damage. However, this may still be important to report.

With reference now to FIG. 32a , a simple absolute value threshold checkof values above 400 Pa would be triggered by both the shockwave and themuzzle blast. The threshold may be raised to exclude non-bullet signals.Alternatively, the largest difference between two adjacent data pointscan distinguish the bullet signal from the non-bullet signal. Forexample, the largest change in pressure for adjacent data points for thebullet is 900 Pa (from the last saturated point at the bottom of theshockwave to the top of the second peak), while the largest single-pointjump for the hammer is only 120 Pa, on the downslope of the path fromthe maximum to minimum values for the signal.

The bullet signal trends have large spikes in the chart of resultingimpact sound such as is shown in FIG. 32a . The spikes in the charts areon the order of 500 Pa in the trial of FIG. 32a . However, in othertrials the bullet signal trends progress from saturated on one end tosaturated on the other end. This is a 1 kPa spike and is typicallylarger than the jumps seen in the shockwaves for those specific trials.Thus, whether it comes from the shockwave or an intense impact sound,any jump near 1 kPa should lead to a conclusion of “firearm impact.” Thehammer signal, conversely, noticeably attenuates after the initialstrike, so the largest deltas of the hammer signal are contained in theinitial strike at 0.197 seconds.

With reference now to FIG. 34, the acoustic data may be used to identifya muzzle blast because of the typical duration of this signal, which isapproximately 2-3 milliseconds (ms). The muzzle blast signal, however,is often peppered with noise from the impact sound, so it is much lesssmooth and much more difficult to isolate. One method to overcome thisis to look at the 200 data points (4 ms) after a threshold pressure isreached, and find the maximum and minimum locations in that vector.

If the data points are more than 2 milliseconds apart, it is likely thata muzzle blast occurred. This method is robust for discerning thegunshot from the hammer trial signal due to attenuation, but could alsobe triggered by the impact noise. The system may have a slope limit toprotect against an inaccuracy in detection and distinguish between themuzzle blast and impact sound which disqualifies the signal from being amuzzle blast if any two points have a difference of more than a certainpressure.

Further, the relative arrival times of a gunshot signal from a singlesensor may be utilized unless more information is known about the event.However, using multiple sensors and cross-correlation can determinegunshot signal times of arrival (TOAs).

With reference now to FIG. 35, a tetrahedral array may be used togenerate multiple TOA measurements. Depending on what informationreaches each individual sensor, the relative measurements allow for thecalculation of the shooter azimuth and elevation angles. The magnitudes(cm) in FIG. 35 are provided to indicate scale.

Typically cross-correlation methods are used to generate TOAmeasurements from data. In the simulated scenario that follows, the TOAmeasurements are the differences in TOA among the four sensors from themuzzle blast, which travels directly from the shooter location to thesensors at the speed of sound.

The muzzle blast TOAs may be converted into differences in traveldistance to each sensor. Then, a three-dimensional grid may be createdwith a direction taken as a parameter to narrow the search. If the useror computer does not have any indication of the direction, [0 0 0] canbe taken. This generates a 10×10×10 m box encompassing the origin,wherein each point is compared to the calculated relative distances.These comparisons yield scores for each point based on the differences.Lower scores indicate a better result.

After iterating through the existing box, the code checks the scoresagainst a tolerance level. If any score is below the tolerance, thesuccessful point is returned as the shooter location. If not, the lowestscore is then used to generate the next search direction, and thefunction is called again. This time a new search box will be generatedbased on the direction, and the process repeats until a successful pointis found. By way of non-limiting example, the scores are plotted on a 3Dgraph, with an arrow leading from the origin to the shooter location. Anexample of a graph plotted using this method is shown in FIG. 36 and inwhich the theoretical shooter location was determined to be [48-67 12].A person having ordinary skill in the art will appreciate that practicalaspects such as measurement errors may be integrated into the algorithm

The initial search direction can be determined with just a slightmodification to the array. First, instead of a regular tetrahedron, thesensors may be arranged as a rectangular tetrahedron as shown in FIG.37.

The azimuth and elevation angles may be calculated in one equation eachand in which ΔT_(XY) is the time of arrival difference between sensors Xand Y. The azimuth angle is calculated from the equation:θ=tan⁻¹(ΔT ₀₂ /ΔT ₀₁)

The elevation angle is calculated from the equation:φ=|tan⁻¹(ΔT ₀₃/√{square root over ((ΔT ₀₁)²+(ΔT ₀₂)²)})|

These equations are based on projections onto the X-Y and Z-θ planes andmake small mathematical approximations. Brute force comparisons havedemonstrated very small differences between the actual directions andthe directions from these equations.

Improvements to the tetrahedral set-up may be considered to account forpractical aspects such as measurement errors. The closer together thesensors are, the more likely they are to be poorly discretized and loseinformation by being clumped into the same time sample. If the sensorsare farther away, the algorithm gets a more accurate reading of theTOAs, especially when the direction of the sound is near parallel to thevector between the two microphones in question.

Conversely, the rectangular tetrahedral system should not exceed amaximum distance of 0.39 meters between the sensors. This upper limit islikely due to the geometric approximations made, which lose validity asthe sensors move farther apart. One way to increase the distance betweensensors without losing the simplicity of the above equations is to add asecond array. Then, the equations can still be used locally while TOAvalues can be cross-referenced against the distance between the arrays.

Shockwave detection with a sensor array only yields an uncertain azimuthprediction. However, in conjunction with muzzle blast detection, thisinformation can yield azimuth, elevation, and distance.

The benefits of using four acoustic sensors are plentiful. By having twosets of azimuth and elevation angles, the system can find the crossingpoint and identify the absolute location of the shooter using justmuzzle blast detection. Meanwhile, the shockwave information becomesmuch more relevant, even by itself. If the bullet passes between the twoarrays, the system can determine azimuth, elevation, distance, bullettrajectory, and bullet speed.

Together, the shockwave and muzzle blast data increases the accuracy ofthe prediction of all of these values as described in FIG. 38. The jumpfrom two arrays to three arrays yields improved accuracy. Likewise, anyincrease above that does the same. Regardless, as these arrays spreadout and increase in number, the localization will continue to improve.

For any acoustic sensor (or array), the line-of-sight to the muzzleblast and shockwave is essential. This immediately eliminates puttingthe sensor or array on any inductive device face perpendicular to theground, as these pressure waves will not propagate through thetransformer and will simply be reflected. Thus, the solution is to placethe sensor or array above the inductive device. However, furthergeometric considerations need to be made. For example, if the lowestsensor only has a two inch clearance above the top of the inductivedevice, both the muzzle blast and shockwave would have to arrive atextremely shallow angles to actually reach it, limiting short rangedetection.

While the muzzle blast will always launch from the location of the shot,it is a spherical wave so a signal will be sent in the direction fromthe gun to the sensor regardless. It should be noted that this signal istypically much weaker away from the line of fire, however, thatdirection is less relevant. Meanwhile, the shockwave will always deployat roughly the same angle relative to the line of fire. This means thatthe shockwave detach point for the part of the shockwave that isdirected at the sensor will occur farther away from the tank, allowingthe signal to gain the height necessary to clear the obstacle.

Furthermore, consideration needs to be made for the location of multiplesensors or sensor arrays. If a second sensor is added, the most obviousresponse would be to place the two sensors above opposite corners of thetop face for the same reasons as above. However, another choice could beto place the sensors on the ground on opposite corners of the inductivedevice so that each sensor (array) services two side walls of the tank.This would allow for better shockwave and muzzle blast detection, butwould almost guarantee that only one sensor (array) would receive thesignals.

Lastly, if four arrays are used, it is recommended that they be placedon the ground at the four corners of the inductive device. Now, everyface has two arrays servicing it, meaning all information can beobtained regardless of the face that is struck. This also guarantees thebullet will pass between two arrays.

If four individual sensors are used, they are effectively serving as atetrahedral array with whatever geometry they are given. It is best tofollow the placement ideas for a single array, while weighing thebenefits of having the sensors spread farther apart.

A next level of complexity for an accelerometer-based system is to haveshot location triangulation based on when the impact arrives atdifferent sensors. This is based on the fact that vibrations from theimpact will propagate evenly in all directions. For the simplest case,it may be assumed that the electrical equipment enclosure or housing ismade of a uniform material with no geometric irregularities.

First, the time delay between every pair of sensors is determined. Whilethis phase delay calculation can be done with cross-correlation, it issimpler to do with threshold detection. This might suggest the use ofthe RMS sensor, but precision time data cannot be lost and theirregularity of these waveforms will be better seen by thecross-correlation using a raw vibration sensor.

By way of example and with reference to FIGS. 39 and 40, trials 5 and 12may be analyzed on a threshold of 0.01 g. For Trial 5, the signalreached both sensors at the same time (or exactly one cycle behind, asthis is what the threshold check yielded). The results suggest that theimpact location was equidistant from the location of the two sensors.For Trial 12, the threshold is reached eight data points later for RV2than RV1. This is a time delay of 156 μs, suggesting that the signal hadto travel a longer distance to reach RV2 by an amount proportional tothat delay.

The time delay can be converted to a distance difference by consideringthe speed of sound in the material of the electrical equipment. Forexample, the speed of sound in steel is 4512 m/s, meaning that a timedelay of 156 μs corresponds to a distance difference of 0.70 m. Thealgorithm then generates a test grid of every point on the inductivedevice. As it iterates through each point, it calculates the distance toeach sensor, and then the difference between the two distances. If thatdifference is within a certain tolerance of the calculated difference,the point is saved as the computer continues to iterate.

With only two sensors, the best precision achieved is a conic sectioninstead of just a single point. The results from trials 5 and 12 aredepicted in FIGS. 41 and 42. The X's in FIGS. 41 and 42 represent thesensor locations 160 and the 0 and square representing the actual shotorigin locations 162 (based on estimation from pictures). In thisparticular implementation, the grid was created symmetrically around thesensors, instead of taking the geometry of the tank into account.

As expected, a time delay of 0 ms from Trial 5 corresponds to a straightline bisecting the two sensors (theoretically this is a conic sectionwith infinite eccentricity). Meanwhile, Trial 12 has a much more definedcurve, demonstrating all of the points that are 0.70 m closer to RV1than RV2. The curve does approach the (approximated) impact location,although ultimately a specific point cannot be suggested. This would besolved by having a third RV sensor, which would yield two more conicsections. The intersection of these three curves would represent thepoint of impact. Theoretically this could still yield two possiblepoints; however, given the known geometry of the inductive device, onewould likely be easily eliminated. A fourth sensor could also beintroduced to narrow down the region of uncertainty.

To the extent that the term “includes” or “including” is used in thespecification or the claims, it is intended to be inclusive in a mannersimilar to the term “comprising” as that term is interpreted whenemployed as a transitional word in a claim. Furthermore, to the extentthat the term “or” is employed (e.g., A or B) it is intended to mean “Aor B or both.” When the applicants intend to indicate “only A or B butnot both” then the term “only A or B but not both” will be employed.Thus, use of the term “or” herein is the inclusive, and not theexclusive use. See, Bryan A. Garner, A Dictionary of Modern Legal Usage624 (2d. Ed. 1995). Also, to the extent that the terms “in” or “into”are used in the specification or the claims, it is intended toadditionally mean “on” or “onto.” Furthermore, to the extent the term“connect” is used in the specification or claims, it is intended to meannot only “directly connected to,” but also “indirectly connected to”such as connected through another component or components.

While the present application illustrates various embodiments, and whilethese embodiments have been described in some detail, it is not theintention of the applicant to restrict or in any way limit the scope ofthe appended claims to such detail. Additional advantages andmodifications will readily appear to those skilled in the art.Therefore, the invention, in its broader aspects, is not limited to thespecific details, the representative embodiments, and illustrativeexamples shown and described. Accordingly, departures may be made fromsuch details without departing from the spirit or scope of theapplicant's general inventive concept.

The invention claimed is:
 1. An inductive device comprising: a tank withtop, bottom and side walls, and wherein each said side wall has an outersubstrate surface; a core having at least one core limb extendingbetween a pair of yokes, at least one coil assembly mounted to the atleast one core limb, and an insulating medium disposed in an internalvolume of said tank; and a coating layer bonded to said tank side wallouter substrate surfaces, and wherein said coating is a polyurea coatingupon reaction, said polyurea coating formed of first and secondcomponents prior to reaction, comprising: a first component comprising amember selected from the group consisting of an aromatic diisocyanateand an aliphatic diisocyanate; and a second component comprising apolyamine.
 2. The inductive device of claim 1 wherein the core has anon-magnetic gap in the at least one core limb.
 3. The inductive deviceof claim 1 wherein the coating first component comprises from 0.1 to 50percent by weight of isocyanates and the coating layer second componentcomprises from about 50 percent to about 75 percent by weight of aminesand the coating second component comprises from about 50 percent toabout 75 percent by weight of amines.
 4. The inductive device of claim 1wherein the coating first component comprises from 0.1 percent to 45percent diphenylmethane-4,4′-diisocyanate by weight and from about 0.1percent to 5 percent methylene diphenyl diisocyanate by weight.
 5. Theinductive device of claim 1 wherein the coating second componentcomprises diethylmethylbenzenediamine andalpha-(2-Aminomethylethyl)-omega-(2-aminomethylethoxy)-poly(oxy(methyl-1,-2-ethanediyl)).6. The inductive device of claim 1 wherein the coating first componentcomprises from about 30 percent to about 60 percent by weight ofisocyanates and from about 5 percent to about 15 percent by weight ofpropylene carbonate and wherein the coating second component aminemixture comprises from about 61 percent to about 89 percent by weightpolyoxypropylenediamine.
 7. The inductive device of claim 1 wherein thefirst and second components are applied to the tank wall surfaces in a1:1 volumetric ratio.
 8. The inductive device of claim 1 wherein thetank walls are formed of a metal having a chemical compositioncomprising by weight: 0%.Itoreq.carbon.Itoreq.0.29%;0.85%.Itoreq.manganese.Itoreq.1.35%; 0%.Itoreq.phosphorous.Itoreq.0.04%;0%.Itoreq.sulfur.Itoreq.0.05%; 0%.Itoreq.silicon.Itoreq.0.4%; at least0.2% copper; and the remainder being comprised by iron.
 9. The inductivedevice of claim 1 wherein the tank material is comprised of a chemicalcomposition by weight percent based on total weight of the followingelements: 0.30% carbon; 1.70% manganese; 0.70% silicon; 1.00% chromium;0.8% nickel; 0.5% molybdenum; and 0.004% boron.
 10. The inductive deviceof claim 1 wherein a coating thickness is from about 0.25 inches toabout 0.75 inches.
 11. The inductive device of claim 1 wherein athickness of the side walls is from about 0.375 inches to about 1.25inches.
 12. The inductive device of claim 1 wherein a reduction in corenoise level of from about 0.1 dB to about 4.3 dB during operation of theinductive device is experienced for the inductive device having a layerof said polyurea coating in comparison to an uncoated inductive device.13. The inductive device of claim 1 wherein said polyurea coating layerprevents leakage of dielectric fluid through openings from about 0.001mm to about 12.7 mm in diameter.
 14. The inductive device of claim 1wherein the coating is applied to outer surfaces of a barrier formed ofconnected plates surrounding a member selected from the group consistingof ONAN cooler, OFAF cooler, radiator, conservator, valve, hose, tapchanger, gauge, sensor, instruments and control panel.
 15. The inductivedevice of claim 1 wherein the coating protects the tank walls frompenetration by an object.
 16. The inductive device of claim 1 wherein ashore D durometer hardness of the coating is from about 50 to about 61.17. The inductive device of claim 1 wherein the tank has at least onestiffener attached to each of the side walls and plates attached to eachof the stiffeners, the plates being arranged to surround the inductivedevice tank.
 18. The inductive device of claim 17 wherein the coating isapplied in a layer to the outside surface of each plate.
 19. Theinductive device of claim 1 having a cooling system comprising aradiator bank proximate to each of two opposing side walls of theinductive device tank, and wherein each radiator bank has a top wall, abottom wall and side walls and at least one fan; and wherein a plate isattached to each of opposing side walls of the cooling system and thecoating is bonded to outer substrate surfaces of the plates.